Jaguar XJ-S. Manual - part 52

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You'll be surprised at the amount of junk that flies out. Thousands of insect wings, bits of leaves, styrofoam,
paper, etc.

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.

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!)”

Instead of the coat hanger wire, Paul Gill says, “A plastic mini-blind slat is great for this.”

Matt Dillon suggests another method: “Take the top holder off of the radiator so that you can spread it apart from the
A/C condenser and clean out the junk that's in between them. I found a whole boatload of stuff in there.” Removing
the upper rail requires removing the air purge tubing, which in turn requires draining a little of the coolant. Think of it
as an opportunity to modify the banjo fitting on the air purge system (see page 187) and install foam to prevent it
getting plugged again (see page 226).

Before you decide that you’re done, try to shine a light through the radiator. You might try laying a piece of paper on
one side and see how much light shines on the paper. The task may still require a mirror and/or a tiny, bright light on
the end of a long, bendable wire, or maybe you can shine enough light through the condenser and oil cooler. If you still
can’t get the enough of the crud out to see light everywhere, it may be necessary to drain all the coolant and pull the
radiator out to clean the fins themselves. Think of this as an opportunity to have the radiator rodded (see page 189) and
to revise the drain scheme (see page 194).

PREVENTING RADIATOR OBSTRUCTIONS: Colleen Melton suggests you install a screen in front of your
condenser/oil cooler to keep crud from plugging things up. “A simple piece of fiberglass window screen (darker color
such as charcoal or black look less obtrusive) run in front of the heat exchangers works great at keeping leaves, bugs,
etc., from clogging up the works. My car has such a screen installed, we've done it on all our vehicles for quite a few
years. Ours is secured at the top by clamping under the A/C drier clamps, and at the bottom by pinching between the
panel below the lower grille and the radiator lower support. Cost is next to nothing and we have more time to work on
other things, rather than cleaning out crud to prevent the dreaded overtemp blues.”

Of course, you could just opt for one of those bug screens that wraps around the nose of the car and clips onto the front
wheel wells.

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.

Unfortunately, it is still made of steel, which means it will eventually rust through again and the rust flakes will plug up
your radiator. Better idea: Call Cathouse Spares in Sydney, Australia (page 689) and order their stainless steel version.
This is one example where an international phone call and overseas shipping are definitely worthwhile.

Mike Morrin went another route: “I could not find a supplier of pre-H.E. expansion tanks. So I eventually had a local
radiator shop make me one in brass, using the original fittings and brackets. He quoted (and I paid) US$130, but I think
he lost money on it because of the labour involved.”

As Morrin notes, there are minor variations between header tanks. Most notably, the pre-H.E. has a fitting on the
bottom for teeing into the line from the heater core to the radiator outlet, while the later cars have a upward-angled
fitting at the bottom front corner for connecting to a fitting on the later crossover pipe right at the suction side of the
pump. If you obtain the later type header tank, you can fit it to the earlier car by simply installing a generic tee in the

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heater hose and running a hose from the upward-angled fitting to it -- or you could spring for a new crossover pipe at
the same time (also in SS from Cathouse Spares) and hook it up as in the later cars.

On later models, the coolant level sensor was located in the header tank instead of the earlier location at the front right
corner of the radiator. If your new header tank doesn’t have a hole for the sensor, drill one about 3” up from the
bottom. If your car has the sensor in the old location in the radiator, relocate it. If you can’t get around to doing the job
properly just now, buy a new sensor and grommet and install them in the header tank and leave the old sensor where it
is. Sooner or later, you’ll probably have the radiator out for rodding and you can have the original sensor location
sealed up at that time.

THERMOSTATS:  The early OEM thermostats had “jiggle pins”, a pin with a rubber ball on one end, loosely retained
in a hole in the flange. They are supposed to be installed with the jiggle pins on the top side.  These probably aid in
either letting the air out while you’re filling the system with coolant, or helping the air find its own way out during
operation.  Clearly, they’re supposed to do more than provide a small leak; a hole would do that. The jiggle pins
evidently act as a sort of check valve, allowing fluid or air through one way but sealing tight the other way. Mike
Morrin provides a theory: “I always thought the jiggle pins were designed such that with the engine stopped, and no
pressure differential across the (closed) thermostat, any air on the engine side of the thermostat could bleed out to the
radiator, but with the engine running the pressure differential would push the pin (or ball) into the hole, blocking any
flow of water until correct temperature is reached.”

It has also been suggested that the pin, jiggling around in the hole, prevents the hole from being obstructed by a small
air bubble. Or that the ball, being much heavier than air but only marginally heavier than water, will reliably fall open
when surrounded by air but can be held shut by the slightest pressure differential when surrounded by water.

Morrin points out that the design got upgraded along the line: “I recently bought a pair of 88 degree thermostats for my
1986 V12 and they are Waxstats and came in genuine Jaguar packaging. The jiggle pin has however been replaced
with a ball in a cage.” Same thing only different, either design will work. Some aftermarket thermostats reportedly
also feature this caged ball (no aftermarket thermostat apparently ever featured the jiggle pin). Jaguar isn’t the only
manufacturer to specify such features in their thermostats; you can find caged balls in several different thermostats on
the rack in the auto parts stores these days.

Try not to buy thermostats without jiggle pins or air bleed valves. If you tell the parts clerk the model year of your car
and he returns with thermostats without such features, try giving him a later model year -- say, 1991. The design of the
cooling system didn’t change, but for some reason some of the computer listings in the parts stores list thermostats
without air bleed valves for early cars and with air bleed valves for later cars. If you must buy aftermarket thermostats
that have no wiggle pins, drill a 1/8” hole in the flange; the small leak might keep the engine from warming up quite as
fast, but at least it won’t drop valve seats due to air pockets. Michael Bucklew suggests “a small cotter pin can be
used.”

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. There are acceptable aftermarket thermostats
available; if you don’t find them at first, try another store.

NOTE: Don’t 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 liquid-cooled
engine without a thermostat.

If you’re in the market for thermostats, make sure to check the computer or applications listing to get the correct type
for the Jaguar; don’t just pick up something that looks right. Julian Mullaney says, “First time around went to Pep boys
and got some new t'stats that looked exactly like the originals. It wasn't until after putting them in water and looking at
the amount of travel they open and the amount of spring compliance on the back close-off disc that I noticed they were
different. They look identical, but they move differently. This is real important because that disc has to close off the
crossover pipe properly. Went back and got some other t'stats that looked the same but had the right amount of travel.
You can check it by taking it out of the package and just forcing it thru the motions to check travel length, etc.”

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This is not to say they must look identical to the originals. Bob Gallivan: “Just received a set of 88 deg C t-stats
(Calorstat made by Vernet in France). These appear to be different than the 88 deg t-stats I replaced last year
(Waxstat).

the vernet came with rubber ring gaskets that fits the outer edge of the disk.

2: overall

length:

Vernet is 51 mm.

Waxstat is ~49.55 mm.

the valve (?) width

Vernet is ~23.25 mm

Waxstat

~17.8mm”

THERMOSTAT TEMPERATURES: The bulbs in thermostats work by taking advantage of the step increase in
volume that accompanies a phase change, in this case when wax melts. Before the wax begins to melt, there is little
plunger movement. As the wax melts, the volume of the wax increases, pushing the plunger out of the bulb and
opening the poppet. Once the wax is completely melted, the plunger stops moving. The temperature at which the
plunger moves is a function of the specific compound of wax used. The small changes in volume with changing
temperature when the wax is entirely solid or liquid are insignificant, and since the bulb itself is changing volume at a
comparable rate, they may not move the plunger at all.

The proper way to mark a thermostat is to indicate its “control range”, the temperature at which it cracks open and the
temperature at which it is fully open -- which, on the Jaguar V12 thermostats, is the point at which the bypass port is
fully closed. However, the thermostat manufacturers generally don’t do this; thermostats are commonly rated with a
single temperature, with no indication whether this indicates the crack-open temperature, the fully-open temperature, or
some temperature in between. The Jaguar literature (including the Haynes manual) does, however, specify “opening”
and “fully open” temperatures for thermostats -- leaving the owner trying to figure out which thermostat in the store
corresponds to the specs. The general consensus seems to be that the “early cars” were originally fitted with 180°F
(82°C) thermostats, while the “later cars” were fitted with 190°F (88°C) thermostats. The change may have coincided
with the introduction of the H.E., but it may have changed at different times between North America and other markets.

The ambiguity in the rating scheme seems to allow for some funny stuff, though. The Robertshaw thermostats offered
by Discount Auto Parts are available in 160°F (71°C), 180°F (82°C), or 195°F (91°C) ratings; their computer describes
the 195°F items as being “closest to OEM specification”, and these are the ones generally kept in stock. Peter Cohen
says, “195°F is the standard opening temp for American cars nowadays. Those responsible for spec-ing products at
certain manufacturers are probably just going on automatic pilot.” More likely, they’re just making thermostats for the
Jag using the same wax bulb used on their products for other cars rather than having to make a separate line of wax
bulbs. Cohen continues: “Beck-Arnley, Motorcraft, and Motorad list 192 degree thermostats.” Perhaps the same idea,
except these companies chose to split the difference between 190°F and 195°F for their wax bulbs!

James Teston says, “F.Y.I: A '92 has as standard (owners manual) 90°C (194°F) but you can get up to 205°F 'stats for
this year. There are no listings this high for the '83.” I just love it when application listings give totally different data
for an ’83 than a ’92, ignorant of the fact that the engine is totally unchanged.

You can apparently forget about relying on the thermostat manufacturer’s qualitative description of the temperature
rating. A review of the offerings of several companies’ 180°F thermostats revealed that many of them described this as
“standard temperature” or “O.E.” (which it is neither for most XJ-S’s), a few described it as “medium temperature”,
while a great many described it as “high temperature” -- an interesting outlook, since it is the coldest thermostat that
should ever be considered for this engine.

There is really little functional difference between 180°F (82°C), 190°F (88°C), 192°F(89°C), and 195°F (91°C)
thermostats, although as noted on page 174 they will result in different gauge readings when the cooling system is

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working properly. In theory, the warmer thermostats should provide better fuel economy, and those who live where it
snows report they will make the heater work quite a bit better.

There are also 160°F (71°C), 165°F (74°C), and 170°F (77°C) thermostats available, generally described by the
manufacturers as “low temp”. None of these should be used in the Jaguar V12. They certainly won’t help anything in
any car, but in this case they might actually cause problems; they may cause the engine to run cold enough that the EFI
system is working on an enriched part of the fuelling map that it was never intended to use continuously, and you may
get bad fuel economy, low power, spark plug foulling, etc. If it gets too far onto the cold fuelling map, it may actually
run rich enough for excess fuel to rinse the oil off the cylinder walls, greatly reducing the engine life. Also note that the
AAV (page 263) won’t fully close until 80°C, so you may also get an inconsistent idle trying to run colder.

The fact that the EFI coolant temp sensor and the AAV are both on the left bank and the left bank runs warmer than the
right bank may confuse this issue a bit. Some people have installed low temp thermostats with no apparent ill effects,
but this might be due to the fact that the left bank is running warm enough to put the EFI in a viable control mode and
to fully close the AAV anyway. If the EFI sensor is moved to the right bank as discussed on page 176 or the cooling
system is modified to eliminate the differential cooling between right and left bank as discussed on page 198, the EFI
sensor and AAV may actually start seeing temperatures as cold as the thermostat spec -- and might start showing
symptoms of running too cold. If this happens, the solution is obviously to replace the thermostats with units in the
180-195°F range.

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 gauge 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

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