S4 Cooling

[MarkS4]

Thinking I am losing more coolant than I should, I noticed the cap with the spring on the swirl pot has 'LBS 13' stamped on it. The guru Steve Heath recommends a 15 lb cap. Could that be the problem or part of it? Where could I get a 15 lb cap?
Mark S4

[GreenV8S]

That's unlikely to be the problem. The amount of coolant loss should normally be negligible, so if you are losing any noticeable amount you need to work out where it's going. Since you have a pressure cap on the swirl tank, the top seal should not normally be under pressure which makes it unlikely you're losing any fluid/vapour there. Any sign of a leak between the swirl tank and the header tank? Is the header tank level correct? The header tank should not normally be full. If you're over filling it that would lead to coolant loss when it overflows in normal operation. Is the header tank being drained back into the swirl tank correctly when the engine cools? A fault allowing the engine to pull in air instead of pulling coolant back from the header could cause the header to overflow.

[DamianS3]

Whilst all good places to look I have to politely disagree with v8s here on my v6 I was leaking from the pressure cap on swirlpot but ONLY when the cap opened to let fluid overflow to the header tank. This is usually pretty evident though as you can see residue on the swirlpot where the leak is. The the swirlpot is clean and stays that way then this is unlikely the cause..

Good luck

Damian S3

[GreenV8S]

DamianS3 said:

on my v6 I was leaking from the pressure cap on swirlpot but ONLY when the cap opened to let fluid overflow to the header tank.

If you leave the pressure cap off the swirl tank completely then I can understand it overflowing, but it should only take a couple of PSI to drive the surge into the header tank. Was there some problem preventing the swirl tank from overflowing to the header tank fast enough, or a cap that wouldn't even hold a couple of PSI?

[RayTVR]

Sounds more like the cap just not sealing properly to me. I had this for a while and solved it with a 'long reach' cap. If you have fluid residue on the top of the swirl pot this would indicate.

[DamianS3]

GreenV8S said:

DamianS3 said:

on my v6 I was leaking from the pressure cap on swirlpot but ONLY when the cap opened to let fluid overflow to the header tank.

If you leave the pressure cap off the swirl tank completely then I can understand it overflowing, but it should only take a couple of PSI to drive the surge into the header tank. Was there some problem preventing the swirl tank from overflowing to the header tank fast enough, or a cap that wouldn't even hold a couple of PSI?

It's a while ago (pre Duratec) but as I understood it the inner cap opened to let expanded coolant flow to the header tank, this was when mine leaked due to poor upper seal. Extra rubber ring solved it pretty well. But still would leak a little.

I them moved pressure cap to header tank and all was finally solved

Thanks

Damian S3

[lewdon]

My car had a similar problem when I first got it. The water level would be fine when I got back from a run but then short of water when I checked it again before I next went out. But none on the garage floor..
I eventually found that the top of the original swirlpot, which is very thin soft brass, had scratched and dented over the years which allowed air to be sucked in instead of the water back from the expansion tank as the engine cooled.
I tried a new rubber seal in the cap but it didn’t cure it completely.
I cured mine by running a bead of solder round the top edge of the swirlpot rim which I then flattened off carefully with very fine wet and dry stuck to a flat piece of plastic.
After that the cap sealed and I haven’t lost water since. Hope this helps.

[MarkS4]

Thanks for the advice, everyone. I thought the lower rated cap was the obvious problem because overflow was coming out via the plastic expansion tank. But maybe not. I will try a few solutions through the coming heat wave summer . . .
Mark