Vapour locks in cooling system

[gdr]

Back to the old problem of cooling. I seem to have a problem with air/vapour getting into the cooling system and getting trapped in the radiator. After fully bleeding (I think) the cooling system, car will run fine in all conditions including traffic for some time, but eventually (after an hour or so) starts to blow water out the expansion tank (which was 1/3 full when cold). Also noticed this happening after some hard trackday use. This happens at relatively low indicated temps, 90C or so. This is not normal expansion, it blows out more than volume of expansion tank. Temperature spikes up to 100C then occur as I think the pump might be cavitating on pockets of vapour and problem gets progressively worse. System then requires bleeding down again which is not fun when hot. Car normally runs at around 80C. Sender is in cyl head. The 3/8" hose from top of radiator should prevent air locks, but its routing alongside main rad pipe as recommended in manual appears to allow an air lock to develop with the car horizontal. By jacking up the rear high (or parking nose down a slope), I get a lot of air coming out of the system.
I've tried various bleeding methods and system appears to be sealed OK (holds pressure).
Has anyone experienced this problem, or got any suggested solutions?
Thanks.

[gdr]

hmmmm. Need to investigate further. Hope its not a head gasket although can be fixed easily enough provided I've not warped a head. Good system pressure makes me think not. Will check the air bleed is not blocked and run with expansion tank empty at cold for a bit, see what happens. I might also rig up an alternative air bleed hose from rad to exp tank mounted slightly higher (along top chassis rail) to see if this helps system degas. Will keep you posted.
Thanks

[gdr]

jschwartz said:

The two caps for the Swirlpot and Expansion tank are different. Make sure they're on the right tank. One has a pressure relief and one doesn't. Can't remember which goes where right now. jeff

Got that one covered - pressure relief cap on expansion tank - but would be bad if you got it wrong way.

>> Edited by gdr on Monday 15th September 19:53