in a Book
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
"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
"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
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
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
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
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
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
"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
"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
"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
"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
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
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
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
Cohen also provides Beck-Arnley hose numbers:
Upper Left 142-4555
Upper Right 142-4548
"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
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
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
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
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
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
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
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
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
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
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
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,
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
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
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
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
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
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
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,
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
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
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
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
"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
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
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
XJ40 and 85-91 V12 201-1151
Four Seasons (Division of Standard Motor Parts)
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
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
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
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
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
HEATER CONTROL VALVE: See the section on the
On to the