Jaguar XJ-S. Manual - part 53

 
 

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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!” 

This is the only failure report on this particular fitting received by this author.  However, this type of failure is not 
unknown, so it’s a good idea to check for them anywhere dissimilar metal tubes are press fit into housings.  If you find 
a press fitting that’s come loose, it’s usually easy enough to drill and tap the hole and install a threaded fitting. 

 

BADLY LOCATED FITTINGS:  The right rear coolant manifold casting has locations for three bosses.  On this 
author’s ’83, the manifold has a vacuum switch in the front boss and the hose supplying the heater is connected to a 
boss in the second; the third is blank, undrilled.  On Jason Philbrook’s ’89, however, there are sensors in the first two 
bosses and the heater hose is connected to the third.  This puts the hose fitting too close to the insulation on the structure 
of the car, and the engine moving on its mounts caused the corner of the insulation to wear a hole in the hose and cause 
a leak. 

See COOLANT CONNECTING PIPE below for ideas on providing new taps along the pipe itself, allowing you to 
plug this one and not use it any more. 

 

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 header tank, where it’s a lot easier to 
get to.  If you have a car with the earlier sensor location, at a convenient opportunity you should relocate the sensor to 
the header tank.  Simply drill a hole in the header tank about 3” above the bottom and insert the existing sensor with a 
new grommet, and find some way to seal the hole in the radiator. 

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

 

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

 

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

Of course, being steel it is subject to rust and corrosion.  The outside merely looks ratty; the inside, which usually rusts 
worse than the outside, dumps flakes of rust into the coolant circuit and helps plug up your radiator. 

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. 

If you need additional openings into the cooling circuit for adding or relocating sensors or taps, one possibility would 
be to assemble copper coolant connecting pipes as described.  Then, carefully noting where there is room for such 
things, you can install a tee in one of these pipes.  A simple “sweat” tee would make an excellent connection for the 

 
 

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heater hose, leaving the threaded openings in the manifold itself available for sensors.  Or, you could solder in a cast 
bronze tee with a threaded connection.  And, of course, you can install more than one tee if it would be helpful. 

Al Askevold has another idea:  Make pipes from Schedule 40 pipe.  But wait a minute!  In copper piping we needed 
5/8”, but Schedule 40 only comes in 1/2” and 3/4”.  Fortunately, 1/2” Schedule 40 has no dimensions anywhere near 
1/2”.  Askevold:  “Schedule 40 is OD 0.840,  ID 0.622,  with a wall thickness of 0.109.”  So, cut 1/2” pipe to length and 
then machine the OD down to 3/4” at the ends to fit the seals. 

But Schedule 40 is ugly!  Yeah, it’s typically galvanized cast iron, and the black iron is just as ugly.  But if you shop 
around, you can find it in solid brass or stainless steel.  The stainless steel Schedule 40 is not very pretty since it is 
unfinished, but as long as you’re machining it anyway you could give it a skim cut over its entire length to polish it up.  
Askevold points out that stainless steel pipe is available from McMaster-Carr (page 708), but the shipping will probably 
bankrupt you; better to buy locally if you can find it. 

 

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 seems to bond 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. 

The top hat seals are expensive if purchased from Jaguar.  There are aftermarket versions available for only a couple of 
bucks each, though; they reportedly don’t have the writing on them.  It’s not known if there is any functional difference 
in the rubber compound, but the cheap items are likely to work fine here -- this is not a difficult connection to seal once 
the rusty pipe issue is dealt with. 

 

COOLANT CONNECTING PIPE SEAL REPLACEMENT:  Odysseus Marcopolus passes along this idea:  “Many 
thanks to Phil Prince's tip about not having to remove either of the manifolds to get the pipe out.  All I needed to do 
was: 

1. Drain coolant. 

2. Remove air filter housing. 

3. Grab pipe w/vicegrips and shove it into the back manifold until the front end was free; then pull forward 

and out.  (I needed to whack the vicegrips a couple of times w/ a hammer to get the pipe moving.) 

4. Remove seals from manifolds. 

5. Cleanup pipe with grinder/wire wheel (just didn't have time to fab something new). 

6. Place new seals in position. 

7. I coated the pipe ends with gasket dressing. 

8. Push pipe into rear manifold until there's enough room to get the front end in and position the pipe. 

9. Refill coolant and replace air filter housing.” 

Of course, this is not likely to work as well with the copper pipe described above as it does with the OEM steel pipe; 
not only will you bugger up the copper pipe with the vicegrips, but the soldered-on shoulders will make it quite difficult 
to push the pipe into the rear housing to remove.  You could, of course, simply leave the shoulders off, since the pipe 

 
 

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should remain in place just fine without them and then you could replace the seals using this method.  Mark the pipe 
with a marker so you can tell when it’s positioned properly at installation. 

This replacement method should work with the stainless steel pipe if you machine the OD of the stainless steel pipe to 
the same dimensions as the OEM steel pipe.  You could even taper the step in diameter to make it work even easier. 

Of course, when all is said and done, it’s not really all that difficult to remove the thermostat housing.  And having 
either the copper or stainless steel pipe in place is likely to avoid the need to replace those top hat seals nearly as often. 

 

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

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

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

Cohen also provides Beck-Arnley hose numbers: 

 Upper 

Left 

142-4555 

 Upper 

Right 

142-4548 

 Lower 

142-0702 

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

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

Regarding the lower hose, Richard Dixon shopped around.  He found one place that offered him P/N C41102 for a 
reasonable price, and another place that offered him P/N CCC6993 for an unreasonable price.  He was given conflicting 
information on whether the later P/N fit only the 6.0 cars or superceded the earlier numbers.  “Called a local import 
parts store and she said $US 14.96 and I can have it tomorrow.  When it comes in, guess what part number it has on it? 
 Both C41102 and CCC6993.  And it fit perfectly.  Go figure!!!” 

By the way, one big issue on lower radiator hoses is collapse.  It’s on the suction side of the water pump, and under 
some conditions (such as a plugged radiator -- and it’s not like that never happens on a Jaguar XJ-S!) the suction can 
suck the hose flat -- which is really bad for coolant flow!  The time-honored fix here is to install what looks like a big 
coil spring inside the hose; many lower radiator hoses come with such coils.  The problem there is that they aren’t 
stainless and eventually rust, which not only allows the hose to collapse but also puts chunks of spring steel into the 
coolant loop.  If this type of thing is in your car, it is suggested that you replace this hose on a maintenance schedule 
rather than waiting for trouble. 

Another solution seems to be to make the walls of the lower hose itself really tough.  The problem here is that, 
eventually, hoses soften up, and may eventually start collapsing -- and you have a really tough time figuring out what’s 

 
 

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wrong with your car, since it’s clearly having cooling problems but you can’t find the fault.  The hose looks fine when 
the engine’s shut off.  Again, replace the hose on schedule rather than waiting for trouble. 

Marty Sullivan came up with the unthinkable solution: a flex hose.  Flex hoses are widely considered unacceptable for 
some reason, but for a lower radiator hose they have some definite benefits.  There is a coil of wire built into the casing 
of the hose itself, where it isn’t in contact with the coolant, won’t rust, and won’t get chunks into the coolant circuit.  
Some people seem to feel they don’t flow well, but there’s little basis for this contention; certainly Sullivan didn’t have 
any problems with flow.  The biggest issue is that, when really old, sometimes a flex hose will delaminate, leaving the 
outside casing and the enclosed wire coil looking fine while the inner lining pulls away from it, collapses internally, and 
plugs the passage -- but this probably doesn’t happen any sooner than the problems with molded hoses described 
above. 

Sullivan claimed the flex hose he found fit beautifully and was much easier to get into place than a molded hose would 
have been. 

If you want the best possible setup, though, the thing to do would probably be to get a good quality molded hose and 
make a stainless steel wire coil to go in it (whether it originally had a coil or not).  You wouldn’t have to worry about 
that hose until it actually sprung a leak. 

If you have an engine heater in the lower hose, all of the above still applies except we’re talking two short hoses instead 
of one long one.  See page 682. 

 

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.” 

 

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 bypass pipe, 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.”