Although there are, at times, a few jerks on this site, you will not find any better information on any possible problem with your Jag that many have experienced prior to you. We have "been there, done that" and will try to explain in detail how to properly do almost (if not all) DIY on your vehicle. If you do elect to take your car in for service and problems (occurring when not needed) you will have to earn enough money to do so as it will be similar to having two wives with unlimited budgets !!!!! lol..... Any problem can be eventually fixed with $$. IMHO, if you really want to fall in love with your Jag, you will have to take care of it yourself.......
Ken in WV

Update - Took the car to the garage last week and they found that one of the radiator caps was not holding the right pressure - so they replaced it

After getting the car back, the needle now consistently sits at the BOTTOM of the "N"- very different from where it was sitting after they did all the major work.

Redgear I am glad to hear that. My problems are still ongoing. They flushed the system and replaced the thermostats to 180 degree ones. Now my system goes to the place you would expect 180 to be , a little below the N. It stays there for a while and you can see some slight fluctuations like the thermostats open and close. The problem is when the cool coolant is exhausted the temp begins to climb up again above the N. So, the system is definitely not able to lower the temp of the coolant well enough after it gets to the radiator. I am pursuing getting my radiator out to rod/recore. I have the Tefba filters to put in to try and prevent a recurrance also.

When was the last time the radiator was out of the car?

If it's been very long, you would be amazed at how much stuff gets lodged in the fins between the a/c condenser and the front of the radiator. The radiator has to be pulled every so often in order to clear all that junk out. Unfortunately there's no way to see if it's blocked without removing the radiator cover, once you've gone that far, you may as well pull the radiator and either get it re-cored or rodded.

Also read the section in Kirby's book about the foam packing that forces air through the radiator rather than around it. It breaks down over the years, or is often completely missing because someone not knowing better has thrown it out.

Good luck.

From what I can tell this radiator has probably never been out of this car. Foam is all in place. The secondary fan runs and the main fan spins although it is hard for me to tell whether the clutch really works. I tried the test of spinning it when it was cold and it only spun a very little bit then spinning when it was hot and I still felt the same resistance. At least there was resistence but I could not tell much of a difference. I think I am just going to replace it to be sure while the radiator is out. They don't seem to cost that much.

There is something odd about the cap on the small tank on the inner LH fender. It has a chain that connects to the end going into the tube that heads over to the fender and to the cap itself. That chain prevents me from taking the cap off because it won't let me turn it far enough to remove the cap to see what is there. Any idea what that chain is for?

When I look in the main cap I do see coolant at the bottom of the fill tube. Although the car had the oddest system I have ever seen on a car. Normally a fill cap is located directly on the radiator itself but this car is completely different. You need a PHd in the XJS to understand it. But I can turn wrenches / spanners so I am hoping I don't run into anything that requires special skills or tools when I am doing this.

Also, there is one other odd thing. There seems to be a vacuum tube that leads to the left fender with a small filter on the end of it that is open on the other end of the filter. Not sure what that would be or why it would be there to draw in air through that tiny filter.

Only the hot test counts. You want no more than one revolution. More than that is 'iffy'....and an iffy fan clutch is a bad fan clutch.




When built the cars used two different caps: one for the filler tube at the center of the engine and one...with the chain....for the header tank. Keeping it chained to the tank means it can't be inadvertently installed on the filler tube. The cap for the header tank is a pressure cap. The one for the filler tube isn't.

In practice, as years go by, a pressure cap is generally used in both locations.

You should still be able to remove the cap, though, even with the chain. On my V12 the cap is chain is attached to the neck so there's even lsack to allow for cap removal. I wonder if someone changed things a bit on your car



"Main cap"? The filler tube at the center of the engine? Good that you see coolant there.




Weird system yes, but a remote 'header tank' isn't all that strange, actually




That the inlet filter for the distributor ventilation system.

That hose goes to the distributor. Another hose at the distributor is connected to a vacuum source. This arrangement pulls fresh air thru the distributor to evacuate vapors....thus preventing a small explosion!

Cheers
DD

Oh. Glad I asked about that one and did not do anything stupid with it. Thanks for the other information as well!