I have a 1981 Jaguar XJ6 and there 2 water caps. One on the expansion tank which stays full, the other is a small tank near the water pump and I have checked it twice after running the car and it is always empty, Is that normal my car runs at 90 degrees. Thanks for any input....Jerry

 

Doug will verify this, BUT, my undestanding is:

That engine cap is for filling the system, and is generally a "blank cap", with the cap on the LH fender tank being the "pressure cap".

Checking the coolant level is via the LH cap/tank.

This is how I did it on the S2 cars. Once the system is filled, that engine cap is basically left alone, and the system is "topped off" IF REQUIRED via the header tank. If I did venture into that centre cap purely for checking purposes, the LH header tank cap was ALWAYS left in place. IF the header tank cap is removed, and the centre cap is removed, the coolant will flow TO that header tank, and OUT of centre tank, that is gravity at its best.

BUT, if that top small container is continously empty, ya got a leak, and that needs fixing.

 

Ok I just did it again I filled the header tank which was empty and the overflow tank full and ran the car and the stopped it and checked the header tank and it is empty and the overflow tank full. The only problem if there is a leak I cannot find any water/antifreeze on the garage floor???? Thanks Jerry

 

Possible start of another blown head gasket... coolant being put into the engine exhaust side?

 

Is there a way to check to be sure, I checked the exhaust and it looked good. Jerry

 

go to a shop that has an exhaust gas analyzer and have them 'sniff' the coolant for hydro carbons.

Or buy a DIY coolant test kit like this

Combustion Leak Detector at National Tool Warehouse

Cheers
DD

 

I will buy the test kit and see what happens. Here is another twist, I fill the header tank while the car was running before it got hot and guess what? The header tank stayed full???? Now I AM CONFUSED.Jerry

 

Ok, now I've gotten myself mixed up. Gah !

"Header tank" on your car is the one at the front of the engine, as you say

"Atmospheric" or overflow tank is the hidden from view inside the wheel well

"Expansion tank" is the metal tank on the LH wall of the engine bay, long neck, has pressure cap, like this:
http://www.jaguarclassicparts.com/uk...expansion-tank


Which is still a possibility!


Cheers
DD

Gah, I meant to quote my own, earlier posting, not edit it. I'm having a rough night!

 

Yes the overflow or atmospheric tank over the drivers side wheel, and the header tank is just over the fan blade. The atmospheric tank has always remain at the same full level. The header tank was empty both time I checked it after running the car. The last time I ran the car I filled the header tank while the car was running but not at temperature(90 degrees) and this time the header tank stay full. Thanks for any help....Jerry

 

Are we talking about the same thing?

Your atmospheric tank will look something like this (this is the V12 version)

Atmospheric Recovery Bottle - Parts For Series III Saloon | Jaguar Classic Parts UK

It's hidden in the wheel well.....the dirty "road side' of the wheel well, not the engine bay side of the wheel well. There is no pressure cap. This is the 'overflow' tank

Cheers
DD

 

I have a couple of picture one in the book and one of my car. The atmospheric tank cap is call an expansion tank in my book the other by the engine motor fan is the header tank cap. I have only 2 caps for the cooling system none on the radiator itself. Hope the pictures will help. Thanks Jerry

 

Very odd combination of parts. The brown tank was used on the 'later design' system which did not use the engine mounted filler cap. The brown tank was both expansion tank and header tank....and of course there was still the 'recovery tank' hidden inside the fender well. This was 1983-ish and later so it wouldn't been seen on your 1981 car and wouldn't be seen with the engine mounted header tank.

There were other minor plumbing differences between early and later systems which might or might not be relevant to your problem.

You still might have a blown head gasket. Or you still might have a situation where coolant is being pushed into the recovery tank (the one hidden in the wheel well) but not be sucked back into the system when the engine cools

Cheers
DD

 

FWIW, I think your car is a later model than 1981. I notice you also have the late style fuel rail, air switching module, and windshield washer bottle. What are the last 6 digits of the VIN?

Also, where your handwritten notes say "header tank" with an arrow pointing to the front of the engine I don't actually see a cap. Can you send a better pic? Very curious !

Cheers
DD

 

I don't have a picture of the passenger side of the engine and won't be back at my shop until Thursday and I can take a picture of it then. Also if you look at the 3 picture it shows the header tank and mine looks just like that. Are you saying there is a third tank, a recovery tank and it is locked in the fender? I thought that was the purpose of the expansion tank. I wish the was a good flow diagram of what everything is doing???Thanks..Jerry

 

If you have the 'header tank' at the front of the engine then you should not have the brown plastic tank at the left side of the engine bay but, instead, the older style metal tank with the long filter neck.

Cars originally built with the brown plastic tank do not have the engine mounted filler/header tank.

It seems that your car has a mix of parts, which might or might not be part of your problem



YES !



Coolant can and does expand into the brown plastic tank. If the brown plastic tank becomes too full, coolant is pushed into the overflow tank hidden in the wheel well

If the hidden overflow tank gets too full the excess coolant is pushed out onto the road....unnoticed while you are driving.

It is very common to over fill the brown tank....creating a cycle of mysterious coolant 'loss'. It should be filled only about half way. Many people have reported that the coolant loss problem went away as soon as they *stopped* adding coolant

Fill the brown tank half way. Drive, recheck, drive, recheck over a few days. If the brown tank stays about half full, that's as good as it gets. The coolant level has stabilized.

Cheers
DD

 

I found a diagram and added it to the original post it show the flow and also the recovery tank. It says it is locked in front of the wheel. I will have a look for it when I get back on Thursday. Thanks...Jerry

 

When you say the brown tank half full you are talking about the expansion tank. I thought my engine cooling system looked like the first picture I posted out of the Haynes repair manual? After checking with the combustion leak test if ok maybe I should drain and flush the system and refill it? Thanks Jerry

 

Yes.

Although, technically, the brown plastic tank serves as both a expansion tank and a header tank. if you have a 'brown tank' system, then you would fill this system via the brown tank



I dunno what you have.

If you have the brown plastic tank you should not have the header tank at the front of the engine.

If you have the header tank at the front of the engine you should not have the brown plastic tank.

If you have both the brown plastic tank *and* the header tank at the front of the engine then some parts have been mixed up during the life of the car.


Flushing is always a good idea every 2-3 years.

*Personally* I would hold off on the hydrocarbon test for the moment. There are other possibilities for the coolant loss that I would investigate first. Let's verify what parts you have on your car first.

The pic shows my old Series III which has the later "brown tank" system. Note that there is no header tank at the front of the engine.

Cheers
DD

 

I will take a picture of the other side of the car on Thursday and post it...Thanks..Jerry

 

I am adding the pictures of the header tank and expansion tank and rough shot of atmospheric tank under the wheel well. I ran the leak test and it was essentially blue there was a very, very small tinge of yellow, I had to put it in a shadow to see it when the vile was held up to the light it was blue. Ever since I fill the header tank while running it has stayed full. I just checked it after running the car for a bit and he header tank is full. So I don't know what went on? Thanks Jerry