Correct radiator cap?

[MissMoppet]

I have been losing coolant for a while but having checked and tightened everything I can find no leaks. I even lashed out a fiver for a new rad cap from a well-known Stag supplier but losses continued. My local village garage has today had a go - gas analysed the exhaust and pressure tested the system - to no avail - BUT saw moisture being ejected from the rad cap (the bottle is kept half-full). He tells me that there are only two sorts of rad caps like this - a long-nose and short-nose. As there is little resistance when putting it on, he feels I may have the short not long cap. But this would mean that the Stag supplier . . . .

Your comments much appreciated.

(Rover engined, Kenlowe fan).

Dave.

[jleyton]

Hi Dave,

It sounds as if you have the Mk 2 system with the rad cap on the expansion bottle ?

If so, it is quite common for leaks to occur between the brass collar and the bottle and for water to be ejected there. That could well look like it is coming from the rad cap.

Cheers

Julian

[MissMoppet]

Thanks. I'm definitey losing coolant - maybe half the bottle every 200 miles - so is there any solution?

[V Mad]

As Julian says it might be the bottle neck leaking. But I buy a lot of rad caps and get quite a lot of rejects that leak, so it could also be the cap.

[73stagman]

Chris will correct me, being the cooling system guru, but I understand the Stag radiator cap should have a relief setting of 20 PSI which will be stamped into the cap. If it is the wrong one it will be stamped with something else! The cap on the tank in my car had no relief spring at all but it now has a 15 PSI cap which is right for the RV8 but not the Stag

[V Mad]

Guru? Oh no, now youve done it Neil.

20 PSI for Mk2, 13 PSI for Mk1. But I would use 20 PSI for all stag engines (unless of course you have that WC stuff in there )

[jleyton]

Some time ago, I replaced my 20psi with a 15psi cap as an experiment, keeping the 20 psi one in the car if needed.

Ever since then, I have not noticed any difference and whilst I appreciate that it means that the water will boil at a lower temperature, I had hoped that the lower pressure might just be a little stressful on components (and me )

Any thoughts anybody ?

Cheers

Julian

Ps Dave - you're not overfilling the expansion bottle by any chance, are you ? It should only be about 1/3 or so full when cold.

[stevestag]

If I put a 20 psi cap on my rover engined stag I lose coolant from the top of the expansion bottle so like Neil I use a 15 psi cap with no problems
Cheers

[MissMoppet]

That's very encouraging. I'll raid the piggy bank and fit a 15psi cap and see what happens. Many thanks to all.