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Modifications Page 1 - Go to Page one two

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Other modifications & upgrades



Overheating Problems
I first thought I had a blown head gasket because air bubbles could be seen in the filler neck. I got a cooling system pressure testing kit and I STRONGLY recommend this, I would go so far as to say essential for a V12 cooling system! Useful fo detecting head gasket leaks (take the plugs out first). Pumping up the pressure in the system and looking for leaks while the engine is cold is much easier/safer. Any weak spots in hoses, expansion tanks, etc. will burst or leak if you over pressurise it somewhat, rather than on the highway. It turned out I had a blockage in a small bore pipe to the inlet manifold. This caused an air lock in the system.

V12 engines can easily overheat if not looked after. This can result in very expensive engine repairs. The XJ-S seems more prone due to having a smaller capacity radiator. Make sure the small gap between the air cond. rad and the coolant rad. is clear. A build up of dead leaves and debtris can accumulate unseen. My car would overheat in standing traffic. The cure and some other measures taken are listed below. I bleed the system when COLD by parking slightly uphill and opening the heater valve. I undo the bleed valve, remove the expansion cap, and the top filler cap (on cross-over pipe). I fill with coolant until the expansion tank is nearly full then cap it. Continue filling until coolant comes up out of the bleed valve and tighten it. Then I continue filling until an inch and a half below the filler cap. The first run will expel some coolant from the expansion tank, but it will draw it back in from the expansion tank when cooling. After that it should be fine, BUT...

An important note about the Pressure Caps
A plain sealed cap is all that's needed on the cross-over pipe, but they can be hard to find. Pressure release is the job of the cap on the expansion tank. Many people fit a pressure cap on the filler of the cross-over pipe, but it MUST have a rubber sealing washer under the TOP part of the cap, NOT stainless spring rings as they will not seal. Alternatively, a higher pressure filler cap than the expansion tank cap could be fitted, but the only cap I could find had a valve in the centre that allowed air back in when cooling. I stopped this from happening by gluing a plain rubber disc over the seal and valve.

Installed black plastic fan
Warning: Don’t use the old white plastic fans – they crack and explode so change it if you've got one!. My (black) fan and clutch came from an XJ-S 6 cylinder engine. A bolt in job, but what a difference in the power of that fan! The old clutch and fan were the main cause of overheating in traffic jams.

Coolant system filters.
See: Jag-Lovers Article and Photos
I’d never had any overheating issues since replacing the fan and clutch, but before doing all the other work on the cooling system, I decided to have a go at making a pair of filters. A piece of copper piping was hammered flat then soldered into a ring. Into the ring I soldered the cone of steel mesh shaped from a domestic strainer. The assemblies are inserted into the top hoses and clamped in place with a normal hose clip (Jubilee clip) hence a strong ring is needed.

The crud collected from just one of the filters after 5 minutes of running the engine up with the car stationary was amazing. I put the filters back in and drove the car for a few days to find even more blockage with quite a lot of larger pieces amongst the debris.

Seeing this prompted me into removing the radiator and high pressure back flushing, steam cleaning and pressure testing.

I also back flushed the engine block and heater with a garden hose. We have quite a high pressure in our main supply. The trick with this is to plug the outlet until it fills up, use a bung on the end of the water hose so the pressure builds up in the block and/or radiator then suddenly release the outlet bung. The sudden explosion of pressurised water really shifts the grunge. I kept this up until the water ran clear both back flushing and forward flushing. If you’re not thoroughly soaked after this, you ain’t done it proper!!

As I said before, I had no really serious overheating problems before the system overhaul, but I’ve noticed an improvement in the efficiency of the heater. Along with the new(used) fan and clutch, it runs much cooler in traffic jams on hot days.

New coolant crossover pipe
Built from standard copper plumbing fittings. The original steel pipe was sound, but rust would build up, so whilst overhauling the cooling system I decided to make a new one. All the parts are available from plumbing sources but I did have a little difficulty finding the large Tee piece. Notice the double elbow I soldered inside it. Where the pipe joins to rubber hose, I simply wrapped a ring of fuse wire near the end of the pipe and soldered it to act as a securing ridge for the hose and clip. This is necessary!!

Brass expansion tank.
Made from steel, they rust and develop pin-hole leaks. Mine was leaking, so a waste of time trying spot repairs. The original was copied by my local radiator repair shop out of brass sheet, but I believe stainless steel ones are available.

New Hoses all round, and belts.
This was a real pain. The problem was gathering together all the correct hoses and belts to fit. I had to go back with two belts as they were two tight. One tip, many modern belts are "toothed" internally. I find these are quite a bit noisier than the older type smooth belts.

Second temperature gauge sender.
I installed in ‘B’ bank and a switch to the temp gauge to read from either bank. I bought a brand new sender and found a discrepancy in the output readings for a given temperature compared to the original. I got another from a scrapyard and it matched the original. Question is, is the new one correct and the two old ones wrong, or vice versa? The moral is check the output of both senders at the same temp.

New thermostats installed.
A warning:-there are a lot of aftermarket ’stats out there that do not do the job. On the V12 it’s not just a ’stat, it’s also a diverter valve that cuts off flow to the cross flow pipe between the banks. If the plate on the bottom of the ‘stat does not cover the cross flow opening, hot coolant from the banks will just go back to the other bank instead of the radiator. Result… overheating. Buy genuine Jag/Daimler parts or measure the new ‘stat movement when hot and compare it to the housing.

Removed Air Pump and associated pipework.
The vanes in the pump had gone and the pipes were blocked. As this was all fitted for emissions purposes originally, I removed it all. The engine doesn't have to turn that pump now. Must have improved bhp, but by how much? A jockey pulley from a later XJ-S was used in it's place (some move the alternator up there).

The holes in the exhaust ports were plugged with some threaded pop-rivets. If you find the right size, they can be inserted and squeezed to tighten with a little exhaust paste around them. The threaded mandrel is then unscrewed leaving a sealed rivet in the hole. No problems with mine.

Handbag” repair to air cleaner flap.
Only the the left hand air cleaner was affected. The diaphragm inside the valve was cooked so it was not diverting warm air from the exhaust manifold into the engine at warm-up. The quicker this engine warms up the better ‘coz there’s a lot of it!

It is held in place by a metal strap that is spot welded to the cleaner body. The strap has to be cut away to release the valve for repair. You will see in the photo that I have left the ends of the strap in place and then I was able to bend them back over the valve canister after it had been repaired. A bit of sealer between the canister and air cleaner body and the job was done.

The diaphragm was repaired in the same way as described for the distributor vacuum advance/retard module. You will see a couple of the self-tapping screws holding the can together. I put a bit of wire insulation over the ends of them as I've caught my fingers on the exposed screws many times.

The vacuum to these valves is controlled by a thermostatic valve between the carb openings in the air cleaner case. Check these are opening at the same temperature on both banks. They are a bit fiddly, but are adjustable.

Jaguar XJ-S steering wheel fitted.
Straightforward bolt on - even the Daimler badge that was taken from the original wheel just slips into the vinyl centre pad on the new wheel .

Modified engine mounting
I modified the left engine mount to avoid torque stress shearing the metalastik joint. Under hard acceleration, this mount is stretched as the left side of the engine lifts with torque. This results in it tearing apart and the modification limits the amount of stretch movement. It was beginning to go and I replaced the other side also. A hole was drilled right through the mount to accommodate a bolt, making sure it would clear the mounting brackets. I found some suitable rubber bushing to keep the bolt cushioned and with washers and nut installed it. I tightened the nut until the bushing was just starting to compress. A locking nut was then tightened against the first nut. No change in the transmission of engine vibration was noticed, but I thought I detected a more ‘positive’ feel when the car was accelerated.


Modifications Page 1 - Go to Page one two

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