For some reason today when I was letting the car warm up (trying to see what temp the electric fans come on at) I noticed coolent starting to drop from the rad cap. I noticed a antifreeze smell yesterday but didn't see a leak. Today though if I let it run long enough in the driveway it starts to leak out at the cap. It's only a month old (the cap) I have checked to make sure it's tight. Any thoughts? As soon as the temp hits the middle of th temp guage it starts leaking.

 

Hi Jordanmc,

Check that the rubber seal on the new cap is not damaged.

Check the pressure rating of the cap as well. (16psi)

Assuming you have a 6 cylinder car.

V12 has two caps of different pressure rating and you can't get them back to front else leaking similar to your problem.

Cheers,

Nigel

 

Thanks. Yes it's a 6. The cap looks fine. I wiped everything clean but yes I guess I should try a new cap first. Can I just grab any cap that 16 or is it specific.

 

Just make sure the cap is suitable for pressurised systems.

New cap, or new old stock cap?

Check that pressure spring on underside of cap is not broken or obstructed.

Also, check that there is no foreign material (dirt, etc.) trapped under the rubber seal.

You could just have that one faulty new cap...

 

I guess the other option is that the car is running too hot and the cap is actually working by letting out the boiling coolent which means my problem could be overheating?

 

What does your temp gauge say?

Cheers
DD

 

Its running right in the middle of the guage. The electric fans are not coming on. While looking at the car tonight I was thinking I should just switch the caps from the expansion tank, see if the leak goes away or moves to the other one

 

Just make sure they're both pressure caps. The one on the engine might just be a blanking cap/filler cap.

Cheers
DD

 

Is the engine header tank cap meant to be a pressure cap or a sealing cap? In one workshop manual it mentions the expansion tank cap being a pressure cap and the header tank cap being a sealing cap. I have pressure caps on both. Is this incorrect?

 

Yes, the pressure cap is opening and there should be a pipe for the X's to bleed to. If not, it just leaks off.


As I recall, there is a tank behind the Left out board lamp for x's to bleed to.


Which "filler" opening has a hose/s that lead there?


Convert one pressure cap to a sealer cap???


Carl

 

Yes the expansion tank has a hose for things to bleed off. I think someone has put a pressure cap where it shouldn't be. The manual seems to call for a sealing cap at the header tank not a pressure cap but everyone I call to order one tells me I need a pressure cap. Very frustrating. I can't get a straight answer.

 

As I recall the one on the engine should be a sealing cap.

It would be Ok to use a pressure cap in that location IF it was higher than 16 psi. For example, if you put an 17 psi cap there, it would effectively become a sealing cap.....as the 16 psi cap at the expansion tank would relieve pressure first and thus prevent 17 psi from ever being reached

Problem is.....16 psi is normally the highest rated cap you'll find

An alternative would be to use 15 psi and 16 psi caps

Or, finding a sealing cap

Cheers
DD

 

The expansion tank should have the pressure cap, and the header on the engine should be a sealing cap. If the sealing cap leaks, check also housing where it seals to and make sure it isn't corroded such as to make the seal not work properly. The housing is steel and has welds on it plus there are normally two small pipe nipples welded on. The housing seals to the water rail with a gasket. Check these aren't the source of the leak too.

 

I agree. The trick now is finding a sealing cap

 

May be some from here.

https://www.summitracing.com/int/sea...erms-_-keyword

Or more usefully

http://www.jagbits.com/category/Seri...Cooling_5.html

 

Google "EAC3424 Jaguar"

Cheers
DD

 

Maybe you have the same problem I had when I replaced the pressure cap on my brown "header" tank and experienced a leak - just like you have. What I found was that the new cap had only one seal, not two as is required.

My brown header tank is plumbed to an overflow tank behind the driver's side wing, as Carl has described. I think that the way it is supposed to work is, that as the coolant expands beyond a certain point, the pressure cap relieves and (1) the coolant flows from the header tank to the overflow tank and (2) as the coolant cools down a vacuum is created in the system and coolant is sucked from the overflow tank back into the system.

But in order to direct the excess coolant to the overflow tank, and then create that vacuum, you need a seal between the lip of the header tank and the cap, otherwise the coolant will escape from underneath the cap and drip from the header tank and you will never get a vacuum.

You can see in the photos, that this particular cap has only the primary (relieving) seal, but nothing to seal the header tank from the atmosphere - just a ribbed steel surface. So I was losing coolant, but never recovering it. The cap is a Quinton Hasell FC56.

I got the proper cap and everything now works as it should.

 

Here is a typical layout for a Series 2. The cap can be seen where it goes onto the housing. This layout was what I had on my 1980 Series 3, but it changed on later Series 3 cars, I believe.

SNG Barratt - The Ultimate Jaguar Parts Specialist