The XJ6 Jaguar
Radiator Expansion Tank

Radiator Expansion Tank

The radiator expansion tank: Some XJ6s have only one radiator filler cap on the header tank while others have an expansion tank with a filler on it as well. On the cars with the expansion tank a lesser known cause of coolant loss and overheating is to have a pressure cap on the header tank as well as on the expansion tank. The cap on the expansion tank should be a pressure cap while the second cap should not be a pressure cap. If you have a pressure cap on the header it will release fluid that will be lost and not recoverable. This constant loss of fluid every time the car comes up to pressure will cause overheating.

Engine Oil

Also here is the filler for the engine oil. The engine requires almost 9 quarts of oil when changing the oil filter. To an American who is used to all engines requiring 4 quarts, this is one hell of a lot of oil. On the other hand with an engine that leaks oil like the 4.2 does it may all be needed. The interesting thing is that if it falls only a quart low it will trigger the low oil pressure light on hard deceleration or hard cornering. Generally this is not a problem as long as the condition only lasts a few seconds. The crank and rod bearings are not supported by oil pressure, they just ride on the surface of a molecule thick layer of oil so as long as the pressure comes right back up no harm will be done. But... you should correct the problem as soon as practical and try to refrain from extreme maneuvering until it is corrected.

I recommend using a synthetic oil. I had a mechanic once tell me that if I used synthetic oil it would cure the oil leaks. I didn't believe him, but since I knew him to be a good mechanic, I tried it. It worked. I don't know why, but it worked. The reduction in lost oil and the fact that I could leave the oil in for three times longer before changing it made up for the increased cost. I now use only synthetic fluids throughout the car.

Carburettors and EFI

The carburetors and EFI are in this area also. The series 1 and 2 cars are carbureated while the series 3 has Electronic Fuel Injection (EFI).

The carburetors require very little maintenance. Keeping the fuel screen clean and topping up the oil in the dampers is all that is required. Some books recommend using SAE 20 engine oil for this purpose. I have used automatic transmission fluid, olive oil, corn oil all with no noticeable difference in performance. Be forewarned that if you use corn oil and spill some on a hot engine part it will smell like you are making popcorn and will keep you hungry whenever you drive.

EFI requires even less maintenance than the carbs. The only maintenance I have done on my '82 XJ6 EFI in 70 thousand miles was to replace the injection hoses that the PO had installed. The injection hoses, the hose from the fuel distribution rail to the injectors MUST be of high pressure type. It looks just like the standard fuel line, but don't use standard fuel line, it wont last. The system is under very high pressure and the hoses will begin to leak very soon if you don't use high pressure hose designed for fuel injection systems.

The first indication (hopefully) that you have a leak is a smell of fuel when you stop the car at the end of a run. The hoses will be leaking onto the top of the head and the heat will cause evaporation that you will smell as soon as you walk around to the front of the car. Don't ignore this or you may have an under hood (bonnet) fire which will really ruin your day. Replacing these hoses is easy and will only require 45 minutes to do all 6 of them. The main thing to remember is to tighten the clamps so that they don't leak under pressure and don't tighten them to the point that they damage the hose.

You should open the hood (bonnet) on a regular basis right after driving the car to look at the hoses. They will be wet with fuel if they are leaking, but 5 minutes later there will be no indication as the fuel will have evaporated. Always replace all 6 hoses together so you know the age of the hose. Using hoses of mixed age just makes for more work in the long run.

You should make it a practice to walk around the front of your car when you exit it at the end of a drive. Doing this just takes a little extra effort and it is worth the information you can gain. You don't even have to slow down as you walk by to notice such things as the electric fan running, the smell of fuel, the smell of hot antifreeze, the smell of a hot rubber hose, the sound of bubbling coolant in the radiator or the sound of steam escaping. Catching these warning signs early will save you much grief. I recently saved myself from a big pain by walking around the front and hearing a hissing sound. I opened the hood (bonnet) to investigate and found a pinhole leak in a radiator hose spraying onto a hot engine. If I had not caught it early I would have had problems a week later and probably not in my driveway where it was easy to repair.

Cruise Control Bellows

The cruise control bellows is a common mode of failure on the series 3 cruise control. The rubber bellows gets loose around the end plates and the vacuum escapes. You can either seal it with silicon rubber sealant or you can use some long "tie-wraps" and wrap around the ends of the bellows to clamp it to the end plates. I have seen three, supposedly dead, cruise controls fixed this way.

Brake Booster and Master Cylinder

The brake booster and master cylinder: I do not recommend rebuilding a master cylinder. It can be done and it is not difficult. I do all mine, but I have been doing it for years. It requires hospital cleanliness, small fingers and sometimes a great deal of patience. But unless you are very sure you know what you are doing you can mess it up. The last thing on your car that you want to mess up is the master brake cylinder. Having an engine that quits is not nearly as dangerous as having a brake system that quits. And besides a rebuilt master cylinder is not that expensive. Someone called me after the first book and said rebuilt master cylinders were not available. I bought one two years ago so either I was lied to, or they were available two years ago. A new one can be had according to this caller at less than $100(US). The time and pain you will save is worth the extra cost.

Replacing one though is easy. First remove as much fluid from the brake reservoir as possible with a suction bulb. Then to remove the master cylinder you need only to disconnect the rigid lines to the cylinder and plug them so they wont get dirt in them. On the series 1 and series 2 disconnect the two hoses to the reservoir and plug them so they wont get contaminated. Now remove the two bolts that bolt the master cylinder to the brake booster.

With the series 3 the fluid reservoir is mounted on the top of the master cylinder and it comes away with the cylinder.

The now famous "assembly is the reverse of disassembly" applies here. Cleanliness is the watchword when working with the brake system. A small amount of contamination can cause brake failure and we don't want that. Remember that any time you open the brake system hydraulic lines for any reason it will be necessary to bleed the air from the system. If you don't you will have NO BRAKES.

Brake Booster

The brake booster is a vacuum servo that amplifies your foot pressure on the brake. If it is working all is well, if it is not, you will have a real feeling of helplessness at the next stop. It is possible to drive the car with the booster inoperative. I once did it for 2 weeks. It is dangerous to do so. The booster allows you to stop the car in half the distance you can under only human pressure. DON'T DRIVE WITH AN INOPERATIVE VACUUM BOOSTER.

There are warning signs when a booster starts to go out. One of the first indications is a sound that can only be described as the sound of one venting gas when you put your foot on the brake. There is no other way to describe it. The second, more ominous indication is the day you are braking for a stop and you realize that it took you more time to stop that you thought it would. Or the feeling that in the last 20 feet of stopping the engine suddenly started pulling and you almost hit the bumper of the car in front of you. Don't wait, drive CAREFULLY to the nearest place where you can get off the road and do so.

The trouble may be as simple as a bad or loose vacuum hose from the engine to the booster.

Some versions of the booster are rebuildable with a kit (aparently all of the series 3 are rebuildable) from the Jag parts house. Other versions are not. If you have a rebuildable unit then I would rebuild it when it fails. It can also be rebuilt by a qualified mechanic for about one half the cost of a new one. A new one is so expensive it will take your breath away. They can be found in junkyards (breakers) and if they are operational then go ahead and use a "previously owned" booster.

Removal of the vacuum booster is easier than the Haynes manual tells you, at least on the series 3 with LHD. I will describe the experience I had when I changed the thing in a hotel parking garage with just my small tool set for traveling.

The Haynes manual says that you have to remove the entire assembly with the master cylinder and the pedal box assembly all in one piece. This requires that the brake system be opened with its attendant bleeding after reassembly. It is also a bitch of a job.

When I read the manual and realized I would have to bleed the brakes by myself I decided to find out if there was a better way. There is, at least on a series 3 with LHD. In looking at other models you may want to make sure that the master cylinder will move out of the way and that you can get to the clevis pin.

First remove the two bolts that fasten the master cylinder to the booster. Then remove the vacuum hose from the booster. Now comes the ticklish part. There is a rubber plug on the side of the pedal box that when removed gives access to the booster clevis pin. There is a rubber plug on both sides, remove them both. Now with a pair of needle nose pliers or a screw driver or anything you can get into the hole, remove the cotter pin (split pin) from the end of the clevis pin. Be very careful here since anything you drop will not be recoverable. Don't drop the pin, or the washers on the clevis pin. Withdraw the clevis pin and the booster is now disconnected from the brake pedal.

Now remove the nuts from the four studs that fasten the booster to the pedal box. Again, be careful here as things you drop may never be found again. Once these are all removed the booster can be pulled forward. It takes a little jiggling and twisting, but it will snake off the studs. The clamps that hold the brake lines to the inside of the fender (wing) well will have to be removed to give you enough slack to move the master cylinder. You will have to slightly, CAREFULLY, GENTLY bend the brake lines to move the master cylinder out of the way. Be very careful here as you don't want to crimp a brake line.

Putting the thing back in is a little tricky as it will only snake back in in one way. Its like those little wire puzzles that when you find the trick are easy, but are impossible without knowing the trick. Just wiggle it around till it goes on. It can help to get one nut on a stud then wiggle the thing around until the remaining studs go in. A slight amount of prying with a big screw driver can help, but you should be very cautious with this it can result in breaking something.

Once it is back in position get the nuts on all the studs but don't tighten them yet. Now re-attach the master cylinder and the clevis to the brake pedal. Again, I warn you, for Gods sake don't drop anything while putting the clevis pin back in or you will have to remove the pedal box to retrieve it. When the clevis is reinstalled with a new cotter pin (split pin) you can tighten everything back up and reinstall the vacuum line and the rubber plugs and top up the brake fluid resevoir.

On to the next part