Hi Everyone,

One thing that has not affected me since driving my 85 VDP in March is coolant loss.

Until a couple of days ago.

When I first purchased the Jag, I checked all coolant hoses as a matter of course. I even replaced one two weeks ago because a bubble of dried coolant on the outside wall of one marked the spot where a crack was developing.

Heck, on first inspection of the car, I had even checked the rubber seals of the radiator cap and was more worried about the correct pressure cap than the very small tear in the outer cap seal.

I am a frustrated airline pilot obviously, as I do a walk around the car every morning and check fluid levels every day.

Two days ago, shock horror, the expansion tank was well below low tide. I topped up, checked all the hose clamps with a flat headed screwdriver but didn't check the seals on the radiator cap.

As I couldn't find loose clamps, dried coolant residue, or oil / water mixed anywhere, I was at a loss as to where the coolant loss was.

The water temp gauge never rose to an alarming degree, so failed head gasket was luckily ruled out as well.

As there was no obvious puddle of water under the car anytime I came back to it, I was starting to wonder if the heater matrix was the suspect.

Yesterday, during morning routine, the expansion tank was again well below a comfortable level.

I topped up and drove for a while, stopped on a flat clean area of concrete and watched for while.

Then it happened. After 5 or 6 minutes, coolant started to seep from the overflow tube. Not enough to draw attention or a big puddle, but enough over seven or eight stops over a couple of hours to significantly drop the coolant level.

I let the engine cool down and removed the radiator cap, this time taking note of the caps' seals.
Needless to say, the small tear from a couple of months ago had worked its' way across most of the seal and another hole had appeared on the other side (or I hadn't noticed it?).

Luckily I had a spare cap in the toolbox, so fitted it, topped up and continued.

This morning, no coolant leak.

It just goes to show how vigilant we need to be as it can sometimes be the smallest things.

When was the last time you checked the seals on your radiator / expansion tank cap??

Cheers and happy motoring,

Nigel

 

Thanks for the post. This is good information. I appreciate the diligence you had in tracking this issue down.

Happy motoring!

Eric

 

I have replaced or rebuilt everything in my cooling system and engine the never gets hot but does lose about 2-300 mls of coolant a week with no traces of a leak. Not really a problem because like yourself I check fluids almost daily and top up where required, I can drive 10 hours straight without needing to top off coolant.
But the expansion tank cap is the one part I haven't replaced until today. Let's see how it goes.

 

Ooo, Clarke! That was Groady! YUK!!
(';')

 

I don't think there was anything wrong with the old one, after a short drive with the new cap on there was a bit of coolant on top of the expansion tank. But maybe I spilt a bit of coolant topping the tank up, will have a better idea when I drive to work tonight.

 

I have the same problem! although one of the caps has 0 rubber on it at all tick this of the list. thanks v much.

 

"I fell in love and I have literally no idea what i'm doing"....

I like this a lot! it defines our passion for these cars.

I went out and checked my cap and the rubber is fine, still this is a great tip - worth keeping an eye on.


Cheers,

 

Your two radiator caps are supposed to be different, the one on the header tank at the front of the engine is a blanking cap,just a flat cap with a rubber gasket inside.



The other cap which is the one we have been referring to is a pressure cap, it is on the expansion tank located on the left inner gaurd,yours may look a bit different to mine as your car is newer. 13 PSI, Repco part No.RC50-13, $10.



I think the traces of coolant I had earlier were where I disturbed the overflow hose,just a small pool of coolant under the hose but the expansion tank neck is dry(after a 40 minute drive in city traffic). Must remember to put a clamp on it tomorrow.

 

When I finally get it home I will have a look

 

Well 10 days and 310 miles and no coolant loss. Who would have thought a non leaking radiator cap would be the culprit.
Would normally put 200-300 mls of coolant in about now.

 

Caps on V12's have been the root cause of so many issues over the years, and new ones are sometimes as bad as the old.

The pressure rating is a tad slack at the China factory me thinks.

I had 15lb caps blowing off at anywhere from 4lb to 20lb. Well known brand, not some "pretend" rubbish.

 

Also to complicate things more, there were two different pressure ratings for the two caps on V12's.

One was tethered to the engine with a chain to prevent a mix up of caps, but over the years....

 

I remember that chain well.

That blank cap that Clarke refers to is just fine for the V12 filler cap, and I reckon we Aussies are the privelaged ones here, since CPC makes them still today. Not sure if that brand/style is available outside our island.

 

I still have the chain, PITA drilling the new cap when your drill press is broken.
Thanks paulyling.