Experience in a Book
Cooling System Maintenance

OVERHEATING DAMAGE: Probably the most notorious cause of damage to the Jaguar V12. In any aluminum-block engine, severe overheating can result in a warped block or warped heads, which in turn normally call for an engine replacement.

In the Jaguar V12, a more common symptom of an overheated engine is a dropped valve seat. Since the heads are aluminum, the valve seats are steel rings that are pressed into the aluminum. Since steel and aluminum have different coefficients of thermal expansion, overheating will cause a loose fit and the seat can just fall out. After that, it holds the valve part way open and bangs around in there. Amazingly, reports of broken valves are rare; more often, the owner who continues driving despite the annoying ticking under the hood allows the valve to beat the seat to pieces, which in turn bang up the piston, the other valve, and the head.

Do not continue to drive when the car is overheating. If no other options are available, drive it short distances at a time, shutting it off and allowing it to cool before starting again.

OVERHEATING -- H.E. vs. PRE-H.E.: Roger Bywater indicates that the pre-H.E. cars had some tendency to overheat: "With regard to the marginal cooling at sustained high speeds the H.E. had a slight advantage in that the higher compression ratio raised the thermal efficiency and reduced the heat losses to the coolant. It was also noticeably over-fuelled at high revs which must have helped further and the problem, slight though it was, seemed to be solved. Distributor build quality was also better by this time."

OVERHEATING: Believe it or not, the XJ-S H.E. does not overheat when it's running right -- and this from an owner who lives in Florida! If yours tends to overheat, don't ignore it; overheating can cause warping in an aluminum block engine, as well as dropped valve seats. Check the following, all of which are described further in this book:

1. Check the radiator for blockage or sludge. Crud in the system will cause overheating under all conditions, but usually more at speed than at idle. Since Jaguar manuals recommend the use of Barrs Leaks, any radiator that has been maintained according to the manual is likely to be plugged.

2. Suspend the thermostats in a pan of water on the stove and bring them to a boil. Do not let them contact the bottom of the pan. If the thermostats are not visibly wide open by the time the water boils, replace them. Their usual failure mode is to open only slightly, which will cause overheating under power more than at idle.

3. Retarded timing will cause overheating under all operating conditions. See the sections on ignition timing.

3a. A seized centrifugal advance mechanism can cause the timing to be retarded at speed while correct near idle, so the car would overheat more while driving.

4. The oil cooler and A/C condenser coil, both of which are in front of the radiator, have a relatively coarse fin pattern. The radiator has a very fine fin pattern. Dirt goes right through the oil cooler and A/C coil and plugs up the radiator.

5. A bad fan clutch causes overheating only in stop-and-go traffic or other conditions where motion of the car doesn't provide enough air flow. The stock fan clutch is a thermostatic type, meaning it engages more to blow more air when the air coming through the radiator is hot. When the engine is hot, rev the engine to 2000 rpm or so. The fan should be blowing hard. If it is just blowing gently, replace the clutch.

6. The fan shroud flaps should be intact and free to flap as intended. If they are missing, overheating when stopped and idling is likely.

7. Front spoiler -- it must be there, and it must be properly mounted.

 

LEAK SEALERS: Mike Wilson says, "Here is what my 1990 XJ-S Drivers Handbook (publication number: JJM 18 02 03/00) states on page 176: "Two 135 ml bottles of Jaguar Radiator Leak Sealer or Barrs Leaks must also be mixed with fresh anti-freeze".

Folks, this horrible recommendation probably ranks as the second biggest problem facing the XJ-S owner after the centrifugal advance seizing problems. Many Jaguar mechanics owe their livelihood to this terrible advice, since a high percentage of their work is traced to this stuff plugging up the bottom half of the radiator and contributing to Jaguar's reputation for overheating problems. In theory, leak sealers will not solidify until they come in contact with air; however, there is always a little air inside a cooling system, and in the case of the XJ-S there is apparently enough to cause trouble. Please, do not use any leak-sealing substance within the V12 cooling system. If the system leaks, fix it.

If the car is more than a few years old and having overheating problems, it's not a bad idea to just take the radiator to a shop and have it boiled or rodded out to restore its effectiveness -- especially if you're not the original owner, and the previous owner may have been using leak sealers. John Napoli reminds you to clean out "the engine block, heater core and don't forget to remove and flush the expansion tank -- these are commonly forgotten repositories of Barrs Leaks."

RADIATOR: The XJ-S radiator is a side-flow radiator divided into a top third and a bottom two-thirds. The coolant coming from the left bank, via the left side thermostat, enters at the top left and flows left-to-right through the top third (it cannot go directly down to the outlet because there is an internal baffle in the radiator). Then the coolant from the right bank comes in, mixing with this already-cooled fluid. The mixture then flows right-to-left through the bottom two thirds of the core and back to the pump.

Because the mixed fluid goes through the pump and to both banks, and the thermostats divert flow rather than stopping it, both banks are always seeing the same coolant temperature and the same flow rate. One thermostat failing would not cause unequal cooling; rather, it would have an equal effect on both banks, and the effect would be less serious than a thermostat failure in a single-thermostat system. Although it is probable two thermostats were used to reduce piping, they do provide some redundancy.

John's Cars offers "super-duty" radiators to fit the XJ-S, including a 5-row unit for the pre-H.E. car. If your radiator needs replacing anyway, it's worth considering.

RADIATOR DRAIN: Up until somewhere around 1988, the XJ-S was fitted with one of the most obnoxiously overdesigned radiator drain cocks in automotive history: a metal drain valve at the bottom right corner of the radiator, operated by a lever that extended up to just below the upper hose fitting. Evidently, the image of luxury is supposed to include being able to drain your coolant while wearing a tuxedo. For all this effort and expense, Jaguar couldn't bring themselves to provide an outlet out the bottom of the car, so opening the drain valve causes coolant to pour all over the structures in the area and dribble out wherever the catch pan isn't. The end of the valve is a spherical shape with a funny flange, making it rather difficult to attach a hose, but it's possible with enough determination.

Somewhere around 1988 -- possibly coinciding with the introduction of long-life phosphate-free coolant -- Jaguar went from the overdesigned drain cock to no drain cock at all. On later cars, it is necessary to disconnect the lower radiator hose to drain the coolant. Wearing a tux is not recommended. In fact, this author once suggested to an owner that he do this task au naturel, and just jump in the shower afterwards.

Even if you have the earlier system with the drain cock, there may be wisdom in disconnecting the hose to drain anyway -- or at least to flush. Plugged up radiators are a staple of Jaguar ownership, and perhaps opening the big hole will flush out more junk than using the tiny drain. Since the drain cock is on one side and the bottom radiator hose is on the other, perhaps the best policy is to use both openings to get as much crud out as possible. Use the drain cock to neatly drain the coolant into a container, and then remove the radiator hose to flush water through.

Before you get too involved with that drain cock, let me provide a description of what you're getting into. The drain cock itself is a solid brass plug valve that turns 90 degrees from full open to full shut. There is a spring on the bottom that "loads" the plug to keep it sealed; the seal is brass-to-brass, there are no elastomers inside the valve. There is also a little diamond-shaped washer that fits on a shoulder with two flats that limits motion to 90 degrees. This valve is probably repairable from most of its typical failure modes, which is an option you may want to keep open; read on before doing anything irreversible.

Unscrewing the valve from the radiator may be the first irreversible thing you do. It is not a tapered thread; it is sealed by a fiber washer. But when tightening down, the valve must end up oriented properly to align with the remote handle. To accomplish this interesting feat, Jaguar appears to have used two tactics: First, the fiber washer may in fact be two or more fiber washers, indicating the assembler may have added washers as required to get the proper alignment. Second, the fiber washers are thick and compressible, so there is some considerable range of tightness that will ensure a seal; the assembler can tighten until it lines up, and leave it.

Of course, you've just unscrewed it. What do you suppose are the odds that it will line up properly and seal reliably when you reinstall it? Fortunately, the size washer needed is the same as those used on many oil drain plugs, so you should be able to obtain a good supply of washers of various thicknesses from local auto supply houses.

If you decide to go ahead and unscrew it, here's a tip: the hex size is 19/32", but if you don't have a wrench that size a 15mm makes a good fit. It may be helpful to unbolt the fan shroud and back it away from the radiator a bit to permit use of an open-end wrench, since even a crowfoot won't work well in this space.

Before you reinstall the drain cock, here's another tip: The hole in the end of the valve is 5/16" to a depth of about a quarter inch, and then 1/4" the rest of the way through the valve. With a propane torch, it is a fairly simple matter to solder a short length of 5/16" OD brass tubing into the end of the valve to provide something to attach a hose to. The hose can then be routed out the bottom of the car, making draining the coolant a lot neater and easier to collect and dispose of properly. Since there's no nonmetallic parts inside the valve, you don't even need to take it apart to solder on it, but you almost might as well -- it's only one cotter pin. Something to keep in mind: the radiator moves around a little on its rubber mounts, the oil lines move around a little with the engine moving on its rubber mounts, and the front subframe moves a bit on its rubber mounts. Make sure there is adequate clearance around the valve and attachments so they aren't subject to impacts or rubbing due to these various motions.

Let's say your valve is toast and you have decided to try and replace it. Go ahead and measure the threads: 13.16 mm OD and 19 threads/inch. As mentioned above, it is not a tapered pipe thread; it's a washer-sealed installation like an oil pan drain plug or a banjo fitting. The closest thing you're likely to find in auto parts stores in the US is a 1/4" NPT (tapered), but it will not fit properly -- it's 18 TPI. Tony Bryant in NZ says this drain fitting is "1/4" BSP (British Standard Pipe). Very common in this part of the world. Cost me less than $1 for a brass plug. Any competent hydraulic fitting supplier should be able to find one, or at least a thread adaptor." Well, here in the Bubba Belt in the good ol' USA, my local hydraulic fitting shop calls it BSPP (British Standard Pipe - Parallel, as opposed to a tapered version) and charged over $5 for a fitting for connection to a 1/4" hose -- and only had that one type of fitting on hand to choose from. The hole through the middle is only about 1/8", so it would drain very slowly indeed; this fitting was clearly designed for hydraulics, not radiator drains.

Bryant also suggests that the coolant drain plug on the block (note: not the one on the radiator) of many Japanese cars is BSP, although the tapered version. Still, the tapered plug may be usable to plug the parallel fitting on the XJ-S radiator.

Another option: find a way to use the original valve as a plug. It's solid brass and very meaty (weighs about five pounds, I think) so it should be easy to work with. One possibility is to cut the valve portion off, just leaving the hex and threads, so it looks like a plug except it has a 1/4" hole through the middle. So, you can put a stainless steel or brass bolt through the middle and tighten a nut down on the other end, and use the assembly as a conventional plug -- just remove the whole thing when you want to drain the coolant. If you wanna get fancier, you can tap the hole in the center for a threaded plug instead of using a bolt.

Or you can get fancier still and install a piece of brass tubing in the hole in the plug, connect a piece of hose to it, route it out the bottom of the car, and plug it with something at the end. Then when you want to drain the coolant, you don't even need to open the hood -- just reach underneath and remove the plug from the end of the hose. You can thread the hole in the plug and screw in a piece of tubing with threads on the end, or you can solder the tubing in the hole. You can stick with the 1/4" hole in the plug, but it might be a better idea to enlarge the hole to 5/16" and use larger tubing and hose; it'll drain quicker and larger chunks of crud can pass through.

A similar idea might be to drill and tap the hex portion and screw in a common fitting. It's too small to fit a 1/4" NPT fitting, but a 1/8" NPT will fit nicely. One might think that draining through a 1/8" NPT fitting would take forever, but believe it or not you can find fittings with 1/8" NPT on the outside and a clear hole through the middle that's larger than 1/4"! One such fitting is made by Brass-Tite!, part number 43275, and has a 1/8" male NPT on one end and a 3/8" hose fitting on the other; it is perfect for this task.

Yet another option would be to make the piece of the original valve into an adapter to fit a standard drain cock. This would involve drilling and tapping for the threads of whatever drain cock you buy. Most of the universal ones seem to fit a 1/4" NPT, but you'll need to choose a smaller drain cock with a 1/8" NPT. You also need to choose your drain cock carefully, since many of them have a moving plug at the inner end that would require more space inside the hole than you'll be able to provide within that chunk of the original valve.

Finally, there is the ultimate fix: toss the original drain cock in the trash and drill out the threads in the fitting on the radiator and retap it for something readily available. The fitting on the radiator appears to be pretty meaty, so it could be drilled and tapped for something considerably larger than the stock drain cock. Of course, this mod will require removing the radiator from the car, but that's not difficult.

RADIATOR AIR PURGE SYSTEM: Across the top of the upper support rail is a tubing assembly for purging air out of the cooling system, and it's attached to the radiator at a banjo fitting at the top right. This banjo fitting has a design defect in that the hole through the side of the bolt itself is too close to the head, so it doesn't line up with the annular groove in the fitting properly. This exact same flaw is found in the banjo bolts on the back end of the tappet blocks and is discussed at length; the same modification should be done here to improve flow and make sure the air purge system works as intended. The banjo fitting on the radiator is longer and has finer threads than those on the tappet blocks, but it is the same diameter.

Using thick copper seals under the head makes the hole misalignment worse, so Jaguar provides really thin seals that tend to leak. Once the modification to the bolt is done, the thick seals commonly found in auto parts stores can be used for better sealing. This banjo fitting requires three seals, and the plug at the top left for venting the radiator when changing coolant requires one more of the same size. If your local auto parts store has a rack of red cards titled "Help!", it probably has a package of sealing washers that are perfect for these fittings: part number 66272, labelled "Brake Hose Bolt Washer". It says they are ID 25/64" and OD 5/8".

RADIATOR REMOVAL: Both the official Jaguar manual and the Haynes manual state that removing the radiator requires discharging the air conditioner freon circuit. They lie. In fact, as Jim Isbell reports, "In the Haynes manual there are 21 steps under section #21 that describe the removal. Steps 1, 3, 5, 9, 10, and 11 are all unnecessary." Most are merely extra work, but discharging the freon is a waste of serious money.

Both manuals also provide the same illustration which shows the radiator sitting on top of the oil cooler. This may be the case for cars that weren't equipped with air conditioning, but for the rest of us the oil cooler is in front of the radiator, and the condenser is on top of it.

Forget the manuals and just dive in. The radiator comes out vertically upward, leaving the A/C condenser and oil cooler in place. Drain the coolant and disconnect the hoses, remove the air purge system tubing from the top of the rail over the radiator, unbolt the A/C dryer from the rail and leave it hanging, unbolt the fan shroud, and remove the rail. Either remove the hood, or simply remove the grille, disconnect the struts, and tilt it forward until it rests on the bumper. Disconnect the hoses from the transmission cooler and the wire from the coolant level sensor (early models only) and whatever other little things are hanging on, and pull the radiator out straight up.

RADIATOR MOUNT BUSHINGS: The radiator is mounted on four rubber bushings, two at the bottom (C43577) and two at the top (C38333). If you wish, you may replace these by visiting your local discount auto parts store and looking through the selection of PCV valve grommets that are usually on a display rack in bubble packs. There is one intended for a Toyota that will serve quite nicely in both positions. It doesn't have as large a weight-bearing surface as the Jaguar originals, but it's not made of British rubber either.

You might wonder why the radiator, which has no moving parts, needs to be mounted in rubber. As any good mechanical engineer will tell you, taking any large mass and mounting it with damping material will go a long way toward reducing vibrations caused by other sources. Rubber mounts render the water-filled radiator a large vibration absorber.

RADIATOR OBSTRUCTIONS: As mentioned above, one possible cause of overheating problems is that the fins have been plugged with crud so air can't flow through. Since the fins in the A/C condenser coil and the oil cooler are coarse but the fins in the radiator itself are much finer, the blockage is often on the front of the radiator -- between the condenser and the radiator, where it's really miserable to get to. John Bertsche provides a procedure: "Well, I really didn't feel like pulling the radiator this weekend. I came up with an alternate plan, which may or may not be useful to those of you with my problem (leaves and debris packed between the A/C condenser, oil cooler, and radiator).

1) Put the front of the car on ramps. Take off the spoiler, if you're lucky enough to have one. Take out the lower splash panel/lower center valence, or whatever you prefer to call it, if it hasn't rotted into swiss cheese from all the wet leaves that have collected between it and the oil cooler after all these years.

2) After liberal use of Liquid Wrench, use your sturdiest pair of vice grips to loosen the two large Philips-head screws holding the oil cooler to the brackets attached to the frame. Once they're loose, you can try using an actual Philips-head screwdriver to take them all the way out.

3) Carefully pry (on the brackets, please, not the cooling fins!) the oil cooler away from the radiator just enough (about 1/4 inch) to get a straight piece of coat-hanger wire (a foot long or so) up in between the oil cooler and the radiator, and gently gently use the coat hanger wire to brush the debris out of the space. If your car is like mine, it will look like the tobacco inside a cigarette (about a carton's worth).

4) Use a blower, like your shop-vac, to blow forward through the radiator (like back-flushing the air flow) to loosen any crud that's trapped in the radiator fins. You can hold the oil cooler away from the radiator a little bit while you're doing this with sticks or whatever (again, levering only against brackets, not cooling fins!). You'll be surprised at the amount of junk that flies out. Thousands of insect wings, bits of leaves, styrofoam, paper, etc.

5) There's quite a bit of space between the A/C condenser and the radiator, but virtually none between the oil cooler and the radiator (at least on my car). So, as you clean out the bottom section, the debris from up above will fall down into the gap you're creating. Make sure you alternate between using the blower and the coat hanger a few times to get everything cleared out.

6) Put it back together and take the car out for a beer. You should notice a big improvement in cooling. I estimate my radiator was about 30-35% blocked.

"I'm pretty sure this took longer to write than it did to do (except for step 6). It may be worth a try (easy fixes first!)"

Matt Dillon suggests another method: "Take the top holder off of the radiator so that you can spread it apart from the A/C condensor and clean out the junk that's in between them. I found a whole boatload of stuff in there."

In fact, this author now recommends the top rail be removed every time the coolant is changed in order to clean out this area -- and perhaps even more often now that long-life coolant requires changes only every five years. It would be a pain most times since the tubing for the air purge system has to come off, but if the coolant is out anyway it's worth the effort. You might even make some changes the first time -- like modifying the brackets for the A/C dryer into 2-piece assemblies and putting spade connectors on the secondary ignition coil -- to make it easier to disassemble next time.

If you still can't get it clean enough, it may be necessary to pull the radiator out to clean the fins themselves.

RADIATOR CAPS: The XJ-S H.E. has two radiator caps, but only the one on the header tank (left side of the engine compartment) is actually meant to operate as a conventional radiator cap; namely, to control the pressure in the system. The one on the bypass pipe (at the top right of the engine) is really just a place to add coolant, using a standard radiator cap because they're available. If one or both of the caps go bad, they may be replaced with standard coolant-recovery radiator caps.

The XJ-S originally came with two different caps that were chained in place to make absolutely sure you didn't mix them up. However, as Alex Dorne points out (and apparently Jaguar figured out), there is no opening out of the chamber between the lower seat and the upper seal in the fitting on the bypass pipe. As a result, it doesn't really matter what pressure rating the cap is you install there; the upper seal will totally seal that opening, no pressure relief is possible. The cap on the header tank will always establish the pressure limit within the cooling system. So, apparently Jaguar now uses two identical caps so it doesn't matter if you mix them up.

Nowadays all radiator caps are coolant-recovery type, but I will point out the difference anyway. In non-recovery systems, any coolant that was relieved by the radiator cap merely blew overboard, and when the system cooled back down air would be drawn back in. Radiator caps made for non-recovery systems usually had a brass diaphragm under the top cover that primarily served as a spring to keep the cap from rattling; it didn't matter if it didn't seal, since coolant was just going overboard and air was being sucked in anyway.

In a recovery system, coolant released is collected in a reservoir and sucked back into the system on cooldown. While the configuration of the radiator opening hasn't changed, it now becomes more important that the top cover of the cap actually seal. When the engine is cooling down and drawing coolant back in, any leaks at this joint will cause it to draw air instead. So, modern coolant-recovery caps have a rubber seal in place of the brass diaphragm. Since this type cap works just fine on non-recovery systems, it is doubtful if anyone actually makes the older style anymore.

HEADER TANK: The header tank is susceptible to rust perforation. The good news is that the later and cheaper tank fits better. The filler is curved to clear the air cleaner that is set forward to clear the ABS unit. The newer tank is about half the price of the older one and has studs instead of bolts to mount it.

Better idea: Call Cathouse Spares in Sydney, Australia. This is one example where an international phone call and overseas shipping are definitely worthwhile.

THERMOSTATS: the Jaguar engine requires little wiggle pins in the thermostats to bleed air out of the system. If you buy aftermarket thermostats and they have no wiggle pins, drill a 1/8" hole in the flange. Install thermostats with the wiggle pins or holes at the top.

The Jag V12 also requires thermostats that have a post on the bottom with a spring-loaded disk for closing the bypass passage when the thermostat is open. Believe it or not, there are aftermarket thermostats purportedly intended for this car that don't have these attachments. Do not buy any such thermostats.

NOTE: Don't try to operate this engine without thermostats. The thermostats must be in place to prevent the coolant from taking a short circuit and bypassing the radiator. Incidentally, it's not really a good idea to operate any vehicle without a thermostat.

THERMOSTAT SEATS: Jan Wikström reports that "The seat of the thermostat bypass (supposed to close when the thermostat opens) in the thermostat housings is subject to erosion. Inspect and fit a bronze seat if necessary." It's not known how common this erosion is, but if significant erosion is present it will definitely reduce cooling efficiency. Jan made a bronze seat by machining a pipe fitting and then machining a suitable recess in the thermostat housing to press it into. Other options would include building up with weld material and remachining or simply replacing the thermostat housings.

Rob Weiss-Malik says, "When I took the t-stats (which I had recently replaced) out again and inspected them I found that the somewhat spherical washer (valve?) at the back end of the t-stats (the one that seats against the coolant return opening when the t-stats open) had very faint off-center circular wear scratches on it. Upon checking the recessed sockets that the t-stat flanges seat into I found that they contained gritty deposits of a grayish material that I could scrape off by using a small flat screwdriver.

"After seeing this I temporarily reinserted the t-stats back in the sockets and it immediately became apparent that they were not seating perpendicular to their sockets!!! This resulted in the back valves not seating the right way against the back opening when the t-stats opened and in turn causing the ring shaped seating marks (scratches). These conditions apparently lead to some of the flow not going to the radiator but going straight back to the engine with a concurrent rise in temperature. Please note that the amount of gritty material at the seats was very small, and yet it caused a large of amount of deflection in the alignment of the t-stats (sufficient to cause bypass of flow). I also religiously maintain the proper proportions of antifreeze in the cooling system, and the radiator was re-cored about 15K miles ago.

"The fix consisted of thoroughly scraping (without scratching) the recessed sockets with a flat screwdriver to remove all of the deposits. This was followed by light sanding with very fine (600 grit) sandpaper. Then the t-stats went back in. Now my gage sits below N and does not creep up into the gray-hair zone.

"By the way, the symptoms of this condition were that the gage would first stabilize a quarter way below N and then would very slowly creep up past the N setting over a period of 15 to 30 minutes. The physical evidence for this condition were the deposits themselves (you can see them easily, assuming you can cram your head that low under the bonnet!!!) and the ring shaped seating marks on the back valve. This was an easy fix and I would recommend it as a routine maintenance procedure whether or not your cat is overheating."

NOT-SO PRESS FITTINGS: Stefan Schulz found that the 1/4" connection on the top of the left side thermostat housing had come loose. This fitting is connected to a hose that goes to the air bleed piping on top of the radiator, and normally operates at cooling system pressure. "The only thing that held it in place was the slight force exerted by the hose pressing on it from above!"

"By the way, Jaguar doesn't sell it as a separate spare part, of course, they want you to buy the entire stat housing and a bit of ancillary plumbing. The quick fix I used yesterday was to squash the pipe using a suitable center punch and a few hammer blows, then force it back into the hole that now was a press-fit again. Still, that doesn't solve the underlying design problem, so tapping the hole and putting in a suitable threaded fitting is what I'll do WIGATI."

This is the only failure report on this particular fitting received by this author. However, this type of failure is not unknown, so it's a good idea to check for them anywhere dissimilar metal tubes are press fit into housings.

AIR BLEED/COOLANT RECOVERY SYSTEM: The diagrams in the manuals show the return line from the heater to the bottom hose fitting on the radiator to go through a tee into the bottom of the header tank. The XJ-S H.E. does not have such a tee; the heater return line goes uninterrupted to the fitting on the radiator. Flow through the header tank (necessary to cause air to bleed into the header tank) is achieved by a line from the tank to the bypass pipe, directly at the water pump inlet.

Normally, each time an engine heats up and cools down, the expansion and contraction draws water back from a recovery tank through a line into the cooling system. However, the coolant return line from the pressure cap to the atmospheric tank behind the left front wheel is quite long. Since the expansion/contraction of an engine only moves a little water at a time, it requires several thermal cycles to bleed the air out of the hose (unless you overheat and blow steam). Each time you open the pressure cap, you allow the water to drain into the atmospheric tank and the line to fill with air. If you keep opening the pressure cap to check the level, it will never get a chance to work properly.

COOLANT OVERFLOW TANK: The overflow container is located directly behind the left front wheel, within the bodywork. To get to it, remove the left front wheel and remove the sheet metal panel at the rear of the wheel well.

The vent on the overflow container is somewhat unusual. On most cars, the container is within the engine compartment, and when it overflows (like, when your car is overheating big time), the fluid coming out the vent just dribbles out onto the ground. In the XJ-S, however, such leakage would result in antifreeze throughout the bodywork -- unacceptable. So, the container has a vent line that is routed out the bottom of the car. For this vent to work as intended, the container must be airtight. The design is really lousy, however, and it is likely to leak throughout the bodywork when overheating anyway.

ANTIFREEZE: Don't operate the Jag or any car without antifreeze in the cooling system. The name "antifreeze" is an unfortunate misnomer, and pure water is a totally unacceptable coolant -- even in Hawaii. Antifreeze not only prevents freezing, it also retards corrosion and crud buildup, helps prevent boilover, and most importantly, serves as a water pump seal conditioner. Running pure water will result in early water pump seal failure. Also, replace the antifreeze annually, because the inhibitors in it wear out and it becomes corrosive.

Scott Fisher sends the following wisdom: "In the context of the automotive cooling system ethylene glycol is not an anti-corrosive agent; it is in fact corrosive. To offset this fact, manufacturers add anti-corrosives (inhibitors) to the glycol. These preparations, while in good condition, perform well in both minimizing corrosion and preventing freezing of the coolant. However, over the life of the coolant the anti-corrosion properties of the inhibitors are depleted.

"Water aids corrosion in three main ways: 1) bringing free oxygen in close contact with the metals so that corrosion (oxidation) can occur. 2) Water is conductive. Once water has been flowing in your cooling system for some time, its conductivity will rise as it picks up metal ions. The water may serve to promote electrical activity which may erode metals by galvanic action. 3) Some of the metal ions in the water may also react directly with the metal surfaces.

"Apart from supporting the above three processes, ethylene glycol has the added unfortunate property that it oxidizes through several stages to oxalic acid. The products of ethylene glycol oxidation by oxygen and subsequent reactions include: aldehydes, carboxylic acid, nitric acid, glycolic acid, glyoxylic acid, oxalic acid, formaldehyde and formic acid. Most of the series of oxidation products to and including oxalic acid are directly corrosive to metals. Added to this, oxalic acid is highly toxic.

"To combat the above acids and other corrosion activity, antioxidants and alkaline formulations are added to the glycol mix. These include many compounds which are used in cooling systems where antifreeze properties are not required and include primary, secondary and tertiary amines; organic and inorganic phosphates, silicates cresols and other phenolic substances; a wide variety of sulfur compounds; soaps; alkali metal salts; and borates.

"These inhibitors slow down the corrosion process caused by the glycol and the water. They may coat the metal surfaces and prevent corrosion by passivation. Passivation is the process where the a protective film forms on the metal which prevents further contact with the solution. Unfortunately, in all coolant preparations (with or without glycol) the inhibitor system (during engine operation) is being continuously depleted in the performance of these actions. For this reason, proper cooling system maintenance is critical.

"One aspect of cooling system maintenance that we can all easily follow is to minimize "aeration" of your coolant. Aerating accelerates the uptake of free oxygen from the atmosphere. As free oxygen is one of the essential ingredients for corrosion, the importance of minimizing it's uptake is clear. To this end you should make sure all your hoses are in good condition and clamped tightly. "Closed systems", where an expansion tank and recovery system closed to the atmosphere is used, also help in this regard.

"If you overheat (boil) glycol-based coolants they must be replaced immediately as this accelerates the oxidization process of the glycol to acids."

LONG LIFE COOLANT: Peter Cohen says, "I noticed that the manual called out "phosphate free" coolant. The statement I am referring to is on Page 26-03 of Volume 2 of the XJS Service Manual (JJM 10 04 06) under the heading "ANTIFREEZE." The V12 HE motor is essentially unchanged since long before the existence of non-phosphate coolant. Ergo, the Jaguar V12 has been doing fine on normal coolant for all these years, so why ask for non-phosphate now?"

"After much searching, the only non-phosphate stuff I could find at the time was Prestone 460 Long Life coolant. The Prestone 460 has the distinct disadvantage of being brown, so now coolant leaks are the same color as oil leaks (and the same color as rusty old coolant). I have since found Texaco Havoline Long Life, which is orange."

Jim Belkoff answers, "Beyond the phosphate-free issue and the long-life issue, Texaco Dex-Cool (and I assume the Prestone equivalent) contains no silicates. From what I understand, silicates are abrasive and gradually eat away at water pump seals. Texaco and GM have done tests to prove this new coolant results in fewer water pump replacements.

"The reason the new coolant lasts so long is the carboxylate inhibitor system that's added to the base ethylene glycol. I would suggest taking a look at Texaco's website (www.texaco.com)."

Use of distilled water must be used or the minerals in the tap water will negate the long-life properties. Belkoff continues, "You should use distilled water with Texaco's Dex-Cool. This stuff is factory fill in pretty much all current GM cars and trucks and the owner's manuals suggest using distilled water. In fact, Texaco sells Dex-Cool in a ready-to-use 50/50 concentration that uses de-ionized water. Considering the stuff lasts 5 years/150,000-miles from new, I think it's worth the extra bother. Also, this stuff is compatible with regular coolant, but the long-life properties are somewhat negated."

How important is this stuff? Apparently we should ask the folks at VW and Saturn. Belkoff: "I don't know about Jaguar, but VW has been specifying non-phosphate coolant since at least 1982." Cohen: "In their first year of production, Saturn recalled and destroyed all of the first cars they sold because "they were shipped with the wrong coolant, which could destroy the engine block". Given that they could simply have issued new motors, this was an impressive waste of money."

COOLANT LEVEL SENSOR: On early cars, it's at the front right side of the radiator, where it's very hard to find unless you have the hood off. Sometime in the early 80's, it was relocated to the expansion tank, where it's a lot easier to get to.

This sensor is nothing more than a pin that makes electrical contact with the fluid itself. The resulting ohmage reading is processed by an electronic gadget, C42294, into an on/off signal to the dash indicator light. If this gadget fails, note that some GM cars use exactly the same type of level sensing system. Their sensor won't fit the Jag, but the electronic box should work.

FINDING LEAKS: Michael Bucklew says there's a product to help. "The item is for checking for coolant leaks on the whole system. A kit comes with a ultraviolet dye that is circulated through system. Shut down, and hand pump up the pressure. With a blacklite the coolant leaks look like neon lights. Typically, kits comes with the lite and dye. I think the price is around 60 bucks at "better auto stores"."

COOLANT CONNECTING PIPE: On top of each head there is a coolant pipe, C42595, that connects a manifold at the rear of the head to the thermostat housing at the front. It is a straight steel pipe with a small shoulder at each end to hold itself and the sealing bush in place.

Of course, being steel it is subject to rust and corrosion. But if you feel like it, there is an easy way to make a nice replacement. Drop by an air conditioning repair shop or supply house, and pick up a length of 5/8" ID (3/4" OD) copper tubing as well as a fitting or two. Note: air conditioning systems typically use the odd eighths sizes of tubing to differentiate them from water piping.

Cut the tubing the same length as the original. Cut the fittings to make rings and use a propane torch to solder them onto the tubing to form shoulders. If you take the effort to polish it up a little, having the copper tube across the top of each head looks really snazzy. Since this tube is mounted in rubber at both ends and has no direct contact with aluminum parts, galvanic corrosion is no more of a concern than in the copper radiator.

COOLANT CONNECTING PIPE SEALS: Part number C37990, commonly referred to as a "top hat seal", is actually the same seal used on the electric fan control thermal switch on the early XJ-S, and may even be used on other types of British cars. This seal can be used only once -- it says so right on the seal itself. When installed and the engine is run, this seal bonds itself to the pipe and makes a very effective seal. Unfortunately, the steel pipe will then rust, eventually breaking this seal. So, every time you're working in this area, you'll probably be well advised to replace these seals while there, cleaning up the OD of the pipe before reinstallation.

Unless you go with the copper pipe replacement described above. In this case, the seal bonds itself very well to the copper, it never rusts, and it can be a real pain to try to pull apart during the next overhaul. Solution: don't ever take it apart again! Since it will never leak if undisturbed, every time the engine is worked on simply remove the entire water rail assembly -- thermostat housing, pipe, and rear manifold -- as a single unit and set it aside for reinstallation later. This will save some money, since the top hat seals are expensive.

RADIATOR HOSES: The hoses in the Jag are not significantly different than any other car. For locations where the shape of the hose is not too critical, go to the local parts shop and ask to look over their selection of molded hoses. Find one with the right diameter, and with a section that will fit where you want it to. It is helpful to have the car there, and a shop that will let you take the hoses out to the car and look at them. Buy the hose and cut it to the length and shape you need and discard the rest. This method is usually cheaper than either buying the Jag hoses or using flex hose, and is very aesthetically pleasing. Note: You will probably not find a hose with the exact same shape as the original. All that is important is that the two ends will connect properly, and that the hose doesn't run into anything in between. Also keep in mind that the engine moves around a little on its mounts, while the radiator stands still; a little room for flexibility in the radiator hoses is helpful.

Peter Smith: "the top left hose is the same shape as (in Australia) a Holden 186 or Mazda 929 late 80's."

Peter Cohen says that the Goodyear catalog lists "a single XJS radiator hose, the one for the upper left. Goodyear part number 61267, cost $6.39. It has a slightly tighter S bend than the original, and appears to be about an inch too long at the front end (so was the Mackay). Same wall thickness as the original. The Goodyear catalog also had a note that this item is also available in "Hi-Miler"."

Cohen also provides Beck-Arnley hose numbers:

Upper Left 142-4555
Upper Right 142-4548
Lower 142-0702

"SICP sells an Australian brand. I didn't like them much. The upper left developed a hole, and the lower was not shaped quite right, so it rubbed on a bolt on the motor, and began wearing a hole in itself. It had to be tie wrapped out of the way."

Auto parts stores offer a wide selection of molded heater hoses too. The question-mark-shaped section of hose that connects the heater return pipe to the outlet of the radiator, CAC 5125, can be neatly replaced by a hose number 303675.

WATER PUMP LUBRICATION: On the top of the water pump is a setscrew with a locknut on it. This setscrew is to prevent the outer race from rotating in the housing, and either inserts into a hole in the bearing or tightens onto a flat. If it inserts into a hole, you can remove the setscrew and screw in a zerk fitting (available at any hardware or auto parts store -- yes, it's even the right thread), and then you can grease the bearings with a grease gun. Be sure to reinstall the setscrew when you're done.

WATER PUMP REMOVAL/CROSS PIPE INSTALLATION: What the Jag manual calls the "cross pipe" is the pipe that connects the two thermostat housings to the water pump inlet, and has the fill cap on top. It is variously called a crossover pipe, a water rail, and several unprintable names. Note that the air balance pipe at the top rear of the engine connecting the two intake manifolds is also called a crossover pipe; try not to get confused.

The repair manuals indicate that the crank pulley must be removed to remove the water pump, but the cross pipe can stay where it is. However, according to Jim Isbell, "The water pump will come out and go back in without removing the crank pulley. But the pump will not go back on with the crossover pipe connected if the pulley is still on as you have to snake it in over the pulley and the crossover pipe would be a big impediment.

"So having said that and realizing that you are now going to replace the crossover pipe with the water pump already installed, there is only one way:

"Lubricate all three of the pipe connections (on the two thermostat housings and the water pump) liberally with 3M water hose sealer. Then lubricate the three matching pipe ends on the crossover pipe with the 3M stuff. Now slip the new, cut to the proper length, hoses onto the crossover pipe. Put two clamps onto each of the three hoses, not tight, just enough so they don't slide off. The two clamps on the right side should be placed so the screw is on top when installed and slightly back. The clamp on the thermostat housing on the left side should be so that it is on the bottom and slightly back so there is enough room for a screwdriver angled down below the header tank. The two clamps on the water pump hose should be on the left side of the hose slightly back so the screwdriver is angled to the left side of the car. If you set the clamps up this way you will save a lot of grief later on.

"Now push the hoses up onto the crossover pipe as far as they will go. Next place the center (water pump), hose onto the water pump tilting it and the crossover into position. It will take a little pushing and prying with a screwdriver, but it's not too bad and the hardest part is done.

"Now, pull all the three hoses into approximately the correct position and lightly tighten the clamps. Now make sure the small pipe on the top of the crossover is clear of the big bolt on the block so that the hose to the overflow tank can be put on without being in a position to rub a hole in it. Tighten all six clamps and you are done."

Lenny Berk did this job, and had the following suggestion: "Removing the engine breather filter housing (two bolts) made my life a little easier to get the crossover pipe in." The breather housing is the thing on the front of the left head, just forward of the oil filler.

Berk also was less than satisfied with the lubricating qualities of hose sealer when fitting the cross pipe. Suggestions for alternatives include water pump lubricant, intended as an additive to coolant. Care must be taken when selecting a lubricant, since the wrong stuff may attack the hose material or otherwise screw up the cooling system.

CROSS PIPE REPLACEMENT: If you've had the cross pipe out, you've probably been alarmed at its condition. It's cheap steel, and usually is so pitted and corroded that it's amazing it doesn't leak like a showerhead. It also is reportedly atrociously expensive from Jaguar, and you really don't want to be searching the junkyards because the ones you find there are likely to be just as corroded. Mark Jackson suggests an alternative: "Cathouse Spares offers a third-part solution. Cathouse can provide stainless steel rails acquired from an anonymous source for about $AUS135 (~$US95) plus the usual costs of mail & handling. I've seen one and it looked pretty good - had all the bells and whistles - just a little "choppy". The angles from memory were mostly welded instead of smoothly bent, but it looked pretty spiffy anyway."

Of course, it's just plumbing. You could conceivably make your own. One possibility is to find suitable copper piping and fittings and solder or braze the whole mess together. The fill cap might be a bit of a challenge, but there's no good reason it has to be a conventional radiator cap; any opening with a suitable watertight cap should work. Or perhaps you could rip a radiator cap connection off the top of a brass radiator and solder it on. The trickiest part may be at the pump inlet itself, where the connection from the expansion tank seems to protrude down the center of the pump inlet connection. It's not known how critical this is, since all lines lead to the pump inlet sooner or later; perhaps a simple cross fitting would work.

You might even be able to replace the entire cross pipe assembly with straight sections of tubing, tees, and suitable hoses and clamps. Note that this is the suction side of the pump, so it might be a good idea to use hoses as short as possible and insert metal coils to prevent collapse.

CROSS PIPE HOSES: John Napoli decided to cut pieces from commonly available hoses to connect the cross pipe. "I did find Dayton hose numbers D71458 (smaller ID hose [to heads]) and D71316 (large ID hose [to water pump]). These were fairly inexpensive. They may not be the cheapest or the best donor hoses to use, but they seem ok. The smaller hose has enough material to cut at least four hoses, and the other two, so I will have a complete set of spares." All of the cross pipe hoses are short, straight sections, so it's probable there are dozens of readily-available hoses that can be cannibalized similarly.

GENERAL WATER HOSES: Harry Trafford suggests better-than-stock cooling system hoses: "Gates makes a cool flexible, wire-inserted hose for bends that would kink regular hose. I think the old name was "Red Stripe", but don't know if the name has changed. The other type I'm using is is Gates "Vulco." No wire, but extremely strong."

A/C V-BELT RUB: If the V-belt rubs against the crossover pipe, it's because the crossover pipe wasn't installed correctly. There are no brackets to hold this crossover pipe in position; it is held only by the hoses connected to it. If it rubs the V-belt, the ends of the crossover were not inserted far enough into the hoses connecting to the thermostat housings. Usually, the clamps can simply be loosened and the pipe pushed into the proper position, and the clamps retightened. Note Jim Isbell's warning above to take care not to install it too far rearward causing the small hose to the header tank to rub on the crankcase breather mount bolt.

WATER PUMP REBUILD PARTS: The Jag water pump seal is an industrial standard; it can be found in any industrial equipment supply store, such as Grainger, as a type 68 shaft seal.

The bearing is also a fairly standard item, similar to those used in many common water pumps. Finding a bearing supplier may be difficult, however. The easiest way to get parts may be to purchase a rebuilt water pump for another type car from a discount auto parts store and remove the new bearing (and perhaps the seal as well) from it. After rebuilding your water pump, return the disassembled pump along with your old bearings for the core refund.

It is possible to order rebuild kits for this pump for reasonable prices.

Despite all the above availability, Dan Jensen suggests you forget about rebuilding the pump yourself and simply buy a rebuilt pump. It isn't that much more money, and unless you have things like presses around it's easy to screw up a DIY rebuild job.

Jensen also suggests you replace the front crank seal and the timing adjuster cover while you're in the area.

WATER PUMP REBUILDING: Some, but apparently not all, water pumps have a single countersunk Phillips screw. According to Thomas Alberts, it is a common mistake to overtighten this screw, resulting in a fracture of the aluminum casting surrounding it. Apparently the casting was designed for a non-countersunk bolt, and adding the countersinking makes the metal too thin for serious tightening. If you wanna make sure the pump doesn't leak, use a good sealing compound, don't overtighten this bolt.

WATER PUMP CORROSION: There is apparently some history of the water pump housing getting corroded; nobody seems to know if it is as a result of pump cavitation, bad antifreeze mixture, or what. Randy K. Wilson says, "The place at which they corrode away is at the lower part of the water pump cavity. This is behind the impeller area, but not the working side of the impeller. The area should be a fairly low flow area on the high pressure side of the pump. But it's close enough to the ouput side of the impeller that turbulence could be present.

"Whatever the cause, I do see the corrosion pitting often enough. There may be a clue in that it's not very often when merely changing water pumps; I see it on engines being rebuilt. Engines get rebuilt because they have done some high mileage, or have been abused/neglected."

FAN TIP RUB: If the tips of the blades on your fan show signs of rubbing, the problem may be in the transmission mount. If you have a metal fan, you can hear it happen: you nail it from a standing start, and get a deafening screech from under the hood like all hell broke loose. A bad, or an incorrectly assembled, transmission mount allows the engine to pivot around on the engine mounts, causing the fan to rub.

A fan tip rub may also be caused by a failure of the left side motor mount. When stomping it in low gear, a lot of torque is applied to the drive shaft. According to Newton, this means that the same amount of torque is applied to the engine/transmission assembly in the opposite direction. The engine tries to tilt to the right, applying tension to the left motor mount that was really designed for compression only. If this rubber mount is torn, the entire engine will lift right up off its mount, causing the fan to rub.

PLASTIC FAN CRACKING: Lee Opausky wrote: "Yes, the yellow plastic fan is cracked at the front. When questioned, the shop foreman of one prominent Jag dealership told me not to worry, the crack on his XJ-S is 1/2" wide!" More proof that you can't trust the dealers for good advice.

Issue 68 (June 1996) of Australian Jaguar Magazine: "Graham Cummins has recently found that the main plastic fan on the H.E. is prone to cracking and breaking up which can cause immense damage under the bonnet." Any guesses as to how Mr. Cummins discovered this problem? Are you gonna find it the same way? Mark D. Stoner did; "My yellow fan decided to explode one day when shifting at full throttle from 1st to 2nd gear. Put a nice dent in the top of the hood along with shredding the steel fan shroud and blowing a huge hole in the radiator."

Jim Isbell ordered a replacement fan, and reports that the fan he was shipped did not look like the original. "It is black and has a flat center metal piece. The old one was white (now yellow) and the center piece was dished. The old one had a lower aspect ratio (short and fat) to the blades while the new one has the higher aspect ratio (long and skinny). The black flat one makes up for the "dishing" by offsetting the plastic instead." With any luck at all, this means that Jaguar has recognized the problem and redesigned the fan, and this new one won't have cracking problems. By the way, some of us believe the original fan was yellow to begin with, not white.

The black plastic fan may be an improvement, but to be safer still it may be preferable to just go ahead and replace the belt-driven fan with electric fans.

FAN CLUTCH: If it is determined that the fan clutch is a problem, there are several possible courses of action: the fan clutch can be replaced with a new one; it can be replaced with a substitute; or the entire belt-driven fan scheme can be chucked and electric fans installed. Your local parts shop is unlikely to carry a Jaguar fan clutch, so you will have to consult a Jaguar parts supplier (and spend some serious cash) to exercise the first option. The second and third options are discussed below.

Of course, you could bolt on a fixed or flex-blade fan and eliminate the fan clutch altogether. However, this results in slightly worse fuel economy and a considerable amount of noise (whine). Most would consider the noise unacceptable in a car such as the XJ-S.

The electric fan is probably the best overall solution, and will result in better fuel economy and more power. There will be slightly more noise at idle, but much less noise at higher RPM. It is unknown why Jaguar doesn't use this system to begin with; perhaps they don't like the sound an electric fan makes. Or, perhaps they want to minimize the use of Lucas parts.

FAN CLUTCH TYPE -- EARLY VS. LATE: The early XJ-S fan clutch mounts with one bolt, the later with four. Mike Morrin points out that his XJ-S manual, "Jaguar XJ-S Repair Operation Manual Incorporating XJ-S HE Supplement published by Jaguar Cars Ltd Publication Part No, AKM 3455 Ed 4 C1984", appeared to have the two confused. "On page 26-3, section 26.35.21 appears twice, once titled "FAN AND TORQUATROL UNIT (Early Cars)" and then titled "FAN AND TORQUATROL UNIT (Later Cars)". The diagrams and text for these sections appear to be transposed, as the section for "later cars" matches my 1975 car (as well as the illustration in the 1980 edition of the parts catalogue)."

On second thought, maybe not. Morrin continues: "I am now sure that the version with the 4 bolts holding the clutch on to the pulley is the early version used on the carburetted XJ12 (and never on the XJ-S), as I now have one of these (XJ12) engines with fan clutch. My "spare" 1973 XJ12 engine has a fan clutch with 4 bolts holding the clutch to the pulley. The clutch has "HOLSET HUDDERSFIED" cast on the front of it. The illustrations both clearly show metal fans."

So, apparently, this is what we have: The early XJ12 had a 4-bolt fan clutch with a metal fan. When the XJ-S was introduced, it came with a 1-bolt fan clutch and a metal fan. In 1979, this was replaced with a 4-bolt fan clutch with a plastic fan.

FAN CLUTCH INSTALLATION -- FOUR-BOLT TYPE: Dan Jensen suggests that, when reinstalling the fan clutch, "Use nyloc nuts on the fan-to-pulley studs. It is a real pain to install both a lock washer and nut on the end of the four studs with very little clearance. Having just a nut to worry about dramatically lessens the problem. I have never had them come loose in any of my three Jags."

FAN CLUTCH SUBSTITUTION -- ONE-BOLT TYPE: The early XJ-S, from introduction through 8/79, was fitted with a fan clutch, part no. T55C, with a single bolt on the front to hold it on. These also used a metal fan blade, C39831.

Mike Morrin notes: "The early XJ-S fan clutch appears to be identical to the unit used on a Rover 3500 SDI. This might not be very helpful in the USA, but they are relatively common in the UK and some other countries. When the fan clutch on my XJ-S was found to be seized, I bolted on the Rover part (no modifications) and have had no problems. The Rover plastic fan is different to the Jaguar's."

It might be possible to retrofit the later type clutch EAC4751 and plastic fan EAC3265 (or the substitutes suggested below) to the earlier XJ-S by purchasing the pulley EAC3438 and the bearing EAC3437. You might also need bushing EAC4382. The question is whether or not the bearing housing is the same, or will at least position the fan properly.

FAN CLUTCH SUBSTITUTION -- FOUR-BOLT TYPE: Later cars used a fan clutch that mounts with four bolts to the front of the drive pulley. This is the prevalent style on US automobiles, leading one to consider the possibility of low-cost substitutes. However, the fan clutch market is full of niggling little details, so one must check several dimensions carefully to make sure a substitute will fit:

A) The pilot hole in the center of the shaft must fit snugly around the stub in the center of the mounting flange. A hole too small won't go on, and a hole too big won't center the shaft properly.

B) The mounting bolt pattern must be workable. This generally isn't too critical, because they all seem to use four bolts and the aftermarket clutches provide radial slots to fit nearly any pattern.

C) The shaft must be of comparable length. Too long will press the fan into the back of the radiator. This dimension doesn't need to be exact, merely close enough to prevent interferences and keep the fan within the shroud for maximum efficiency.

D) The bolt pattern for mounting the fan to the clutch must match.

E) If the fan has a recess for the clutch housing, the clutch housing must fit within the opening.

The auto parts houses normally have a cross-reference chart that lists the above dimensions for the fan clutches available. If you compare the clutch from your car to their chart, you can determine what can be used. David Johnson found a substitute, a Hayden 2747. "This is a Ford/GM heavy duty clutch, all the dimensions match except it is a little longer, i.e. the clutch bolts on directly with no modifications. The existing fan will bolt directly to the clutch. The advantage of this clutch is that it will turn at 90% of the pulley RPM. The standard duty units only turn at 75% of the pulley RPM."

Now, if you have replaced your yellow fan with the later design black plastic fan -- or wisely plan to (see the section on fan cracking) -- Johnson has bad news: "The two fans (yellow and black) are interchangeable if you have the original Jag fan coupling. The GM fan coupling I stated was a replacement, only works with the yellow fan because the centre boss is a larger diameter (approx 7.5 inches). The black fan is OK with the jag clutch coupling, but will not fit the GM fan clutch substitute, because the black fan centre boss is only 6.5 inches diameter, i.e. the GM fan clutch fouls with the fan blades. I went out this weekend in search of a clutch coupling for the black fan, but cannot get an exact match with the Jag original, because all the ones that fit the bolt holes and centre boss are more than 6.5 inches in diameter."

If you find a clutch that is suitable except the pilot hole is too big, it would be a simple matter for a machine shop to fabricate a bushing to adapt. Some Jaguars come with such a bushing, EAC4382; perhaps this bushing can be used to adapt an aftermarket clutch. Its ID is 5/8", OD is 3/4". Michael Neal suggests you be sure the bushing is correct and necessary before pressing it into the clutch, since it can be difficult to remove.

If you find a clutch that is correct except for the fan mounting (or the problem with the black fan not fitting the aftermarket clutches), you can replace the fan along with the fan clutch. A procedure is described below.

1. Go to your local junkyard and buy a fan that fits the clutch, basic Ford or Chevy; preferably with unequally-spaced blades (reduces whine) and preferably with aluminum blades (easier to cut).

2. Trim the tips of the new fan until it is the same diameter as the original. After cutting, round the corners and file the edges for safety.

3. Bolt the sucker together and check for interferences. Noted possible interferences include the water pump pulley and an oil line across the bottom. The oil line may be bent and repositioned, or both interferences may be corrected by trimming or notching the blades. Obviously, trim all blades exactly the same way. It's helpful to cut out a cardboard template the shape of one blade and use it to mark each blade for trimming.

4. Remove the fan from the clutch. Set the fan on razor blades centered on opposing bolt holes to check the balance. Trim a little metal from the blades on the heavy side until it balances. Rotate 90ƒ and balance the other way. Make sure it balances both ways when completed.

A fan clutch that has the same pilot hole diameter, a slightly longer shaft length, and a different fan bolt pattern was found at AutoZone. It is made by Imperial, part number 215038. Since the offset of the mounting flange of the junkyard-purchased fan was less, the fan blades themselves end up in exactly the same place. The longer shaft also makes it a lot easier to get the mounting bolts in. It is believed this clutch, with a modified fan from a junkyard, will fit all the XJ-S's from 8/79 on.

Since the aftermarket clutch was designed to turn a 19" fan while the original turned a 17", the aftermarket clutch engages more forcefully than the original. This assembly will therefore make more noise (whoosh) than the original. But it will reliably keep the engine cool.

Some aftermarket fan clutches come with a lifetime warranty. But even if yours doesn't, you still can replace it much more easily next time, since you will already have a suitable fan and/or bushing.

FAN BEARING: The fan on an XJ-S is mounted on a dedicated bearing instead of on the water pump as in most cars. The bearing appears to be similar to those found in several types of water pump, except the shaft on one end is too short to mount anything on. Perhaps a suitable water pump bearing can be found and the unused portion of shaft cut off (be careful not to get the shaft too hot and damage the seals!). Since finding the bearing itself may be hard, perhaps the most expedient procurement method would be to buy a suitable rebuilt pump, remove the bearing, throw the remains of the new pump along with the shot Jag bearing back in the box and return it for the core refund. Some rebuilt pumps available in auto parts shops are really cheap.

A better alternative is to chuck the engine-driven fan and install an electric fan. See comments below.

IDLER PULLEY BEARING: The repair manuals indicate that the idler pulley for the fan drive belt is attached to its support arm with a nut within a recess on the back side. On the author's '83, the assembly looks just like the pictures except there is no nut; the end of the shaft is flush with the surface within the recess. Apparently the bearing itself is not intended to be replaceable; the parts suppliers offer only the entire arm/pulley assembly, EAC8097.

Bernie Embden reports that the early arms were made of aluminum; later idler arms are iron. Bernie's car is a '78 (and has a nut), so apparently the early design was used at least that late. Mike Morrin has two early cars and one has a nut and the other does not, but both have aluminum arms, so there are apparently at least three configurations: Aluminum with nut, aluminum without nut, and iron without nut. "The 1980 XJ-S parts catalogue shows the part number of the assembly as being C39875, with no separate part numbers for the pulley or arm (and no nut)." This might be the aluminum without nut part number, with the EAC8097 reflecting the change to iron.

Daniel Pontes had a shot bearing in the idler pulley, and rebuilt the water pump thinking that's where the noise came from. "This pulley mounts on the water pump so a stethescope is useless. Disconnecting belts and running the engine is also a waste of time. The only way to track the source is a manual shake with your hands on each and every pulley.

"A few phone calls later I find out that this pulley is very costly and very hard to come by. Since it is only the bearing that goes I thought it should be no problem to put a new one in. Yea right!! My fix-

1. find a new FAG bearing # W52315-1.

2. Have your machine shop press out the old bearing out of the pulley, mark which side faces the front.

3. The shaft is only peened onto the arm, it comes out easy enough.

4. The new bearing has a long and short shaft on either side of the outer race. This is a water pump bearing and the shaft is the inner race.

5. Have the machinist chuck the long end into a lathe and dress the short shaft to fit into the idler arm.

6. Press the pulley back on with the front side facing the front.

7. The goal is to get the pulley as close as possible to the arm without rubbing.

8. Press the pulley with the new bearing into the idler arm.

9. Do not peen this bearing onto the arm. It will break. TIG weld it into place-- it can always be drilled out if it fails again.

10. Cut the long end of the bearing shaft as close as possible to the outer race of the bearing and dress it .

11. Install your new idler."

Of course, welding is not likely to be good for the seals and lubricants within that bearing or the temper of the shaft -- and would be especially difficult if the arm is aluminum. Perhaps while the machinist is working on dressing that shaft, he can provide a retention scheme -- like threading it for a nut.

Note that the fan clears the front of this assembly by only a small amount, so it may be advisable to check the clearance of the new assembly by spinning the fan around by hand before starting the engine.

ELECTRIC COOLING FAN: Yes, it's atrociously expensive. But it doesn't do anything any other 12V, 11" diameter electric fan won't do; substitutions are in order. Be sure to include a system of rubber mounts, similar to the Jag originals, to minimize noise.

One possibility is to buy the 11" electric fan from J. C. Whitney, 38xx3020A, remove the fan/motor from the shroud, trim the blade tips as required (1/8" or so) and figure out how to mount it. Depth won't be a problem, it's really flat. But you don't really have a good opportunity to look at it before you buy it to decide if you can make it fit.

A Subaru fan will work with minor blade trimming and a homemade mounting adapter plate. The bad news is that a Subaru fan ain't cheap either, but at least it can be found in a common junkyard.

Alex Dorne fit an electric fan from a Saab 900 Turbo and says it "replaced, and even looked better, than the original when in place. The diameter was perfect, giving about 1/4 of an inch air around the propeller. And after removing a metal protective ring around the prop I could use what was left of the mount and bolt the fan to the shroud using the upper rh and lower holes. I also think this fan flows more than the original since it's designed to cool a Turbo engine all by itself."

"I also remember someone told me years ago (>10) that the turbo fan motor is flatter than on the non-turbo because the lack of space between the radiator and the engine which had the turbo mounted near the rear of the engine (i.e front of the car!). It makes sense, doesn't it? Anyhow, the flatter design leaves even more space between the fan and the engine in the Jag than the original fan did." Note: this author looked at Saab 900's in a junkyard and can confirm that the Turbo has a suitable fan while the non-Turbo is nowhere near as appropriate.

John Goodman reports that the XJR-S has a different 11" fan than the basic XJ-S: "Seven blades high CFM part no. EBC 4553. No part no. listed for the fan shroud so would imagine it could be retrofitted." You can draw your own conclusions about why Jaguar would go to the effort of providing a different fan.

ELECTRIC COOLING FAN SWITCH: There are apparently at least three different switches that have been used in the XJ-S. Up through VIN 101854 (mid-'79), switch EAC1322 pressed into a rubber grommet in the water pump inlet. I think this type of switch is called an "otter switch". From VIN 101855 to VIN 151087, switch EAC2510 threaded into roughly the same location on the pump inlet, so clearly the pump inlet was changed to provide a threaded hole. After VIN 151087, switch DBC2145 was used. It is unknown what the difference between the last two switches is, since they both fit into a threaded hole; perhaps they turn the fan on at different temperatures.

Concerning what is probably the latter switch, Peter Cohen reports: "Beck-Arnley lists the same part number for the 85-91 XJ-S V12 as for the 88-90 XJ40. This part is actually an XJ40 part. It has two wires that are potted into the switch itself, leading to a cylindrical plastic connector (2 inches long by 1 inch diameter). This part can be used in the XJ-S V12 by cutting off the connector, and attaching blade connectors to the switch wiring. This part may also be correct for the 92-96 4.0L XJS 6 cyl.

"The Jaguar dealer quoted $122.50 for the XJ-S switch. SICP lists it for $66. The Beck-Arnley part is just under $30. Here are the catalog listings for some other sources for XJ40 fan switches that should be in the same price range:

Beck-Arnley
XJ40 and 85-91 V12 201-1151

Four Seasons (Division of Standard Motor Parts)
XJ40 36538

NAPA
88-90 XJ40 FS-222

Note that the original switch has connectors right on it -- which is a real pain to get the spade connectors on and off of. Since this XJ40 switch has wires that you put spade connectors on the end of, it should be easier to connect the harness to.

Would the XJ40 switch replace both the DBC2145 and the EAC2510? Unknown. However, Cohen claims the elbow itself, EAC3195, apparently didn't change, so it should thread in.

If you have an early car, do you really want to put in a new otter switch? Well, if it were my car, I wouldn't. Instead, I'd consider buying a new pump inlet EAC3195 (or threading the hole where the rubber grommet went) and fitting the later switch.

LATE MODEL ELECTRIC FAN OPERATION: Bruce Segal reports: "I believe Jaguar changed the design in 89 so that the fans no longer come on with the A/C compressor." Wise? Many owners don't think so, and rewire the fan the way the earlier cars were wired so the small electric fan comes on with the compressor.

FAN SHROUD FLAPS: At the lower left corner of the fan shroud are a couple of rubber flaps. These are designed to allow air to flow rearward through the openings in the shroud but not forward. At speed, the air coming in the front of the car and through the radiator merely blows these flaps open. At a standstill, when the fans are trying to draw air through the radiator, these flaps shut to prevent the fans from drawing air from the engine compartment instead.

They're as simple as they look. If they are damaged or missing, it is easy enough to make replacement flaps from an old inner tube, or even old shoe leather.

FRONT SPOILER: It's important to have the front spoiler in place. Engine cooling relies on air coming in through the radiator, and it must have a place to go. The XJ-S does not have vents through the hood or out the sides, so all this air must go out the bottom. The front spoiler is designed to direct air either into the radiator or around the sides of the car, and to restrict air from going under the nose of the car as much as possible. This results in low pressure under the car, so the air going through the engine compartment can easily flow out that way.

However, if the spoiler is missing, air can flow right under the nose of the car unimpeded. This increases the pressure under the front of the car, which in turn resists the outflow from the engine compartment. The air coming in through the radiator cannot escape as easily, and builds up pressure in the engine compartment. The resulting backpressure prevents as much air flowing through the radiator. It also tends to cause significant lift on the front end (try multiplying a very small pressure over the entire area of the front half of the car; the total lift can be very large indeed) and can cause the car to "wander" at high speed.

KEEPING THE IGNITION SYSTEM COOL: Possibly the worst area for heat problems is within the "V" on top of the engine. Early XJ-S's had so much trouble with cooking the ignition amp that Jaguar created a relocation kit to move it out of this area. Cracked distributor caps have been a problem. Seized centrifugal advance mechanisms are a problem. The wiring harnesses within the V always seem brittle. All of these are symptoms of excessive heat.

Maintaining a good airflow through the engine compartment does wonders for minimizing such heat-related problems on components. However, airflow to the V is largely blocked -- not by the A/C compressor so much as by the plate supporting the front of the compressor. See the Air Conditioner/Heater section for notes on correct installation of this plate.

One simple way to improve things would be to cut a big hole in this plate. Be careful to leave enough metal to properly support the compressor, but this will still allow a substantial opening. Since this area is directly behind the main fan, the hole should allow some airflow under the compressor and throughout the V area.

HOOD VENTS: See the section on Body Modifications.

HEATER CONTROL VALVE: See the section on the Air Conditioner/Heater.

On to the Fuel System