Coolant pressurisation, help!

[MartyMcfly]

Hi, I have just bought a speed boat and dont really fancy dipping the back of my Subaru in the sea everytime i launch her SO I have my eye on a 1995 3.0 SSRG, its done 120,000KM/74K miles, it is from a dealer and is priced at £1200 with a "needs some attention please ask" sticker in the window, is very tidy but has one major OR minor problem! "intermitiantly" after say 15-20 miles it suffers from coolant pressurisation forcing the fluid from the radiator up to the expansion tank and then proceeding out of the overflow.

It has litterly just had a new cylinder head fitted by a VERY GOOD 4x4 import mechanic (the dealer), and he cant off the top of his head think on what the problem could be?

I have heard rumours about Rad caps lifting and then never re-seating/releif valves needing replacement ect? although obviously it is more likely to be a problem with the head/gasket?

Any advise would be VERY MUCH appreciated

Many thanks

Mart

[charvell]

could be air locked or the head is a duff one

[NiftyNev]

Could be an air lock as stated if heaters were not on when cooling system was filled or dud radiator cap or thermostat. Could be the head bolts were no replaced and the head not torqued down correctly because the bolts were stretched. There's a number of things that need checking.

Nev

[Sancho]

Personally, I wouldn't buy a surf from a 'very good' mechanic who was unable to diagnose what is, in the scheme of things, a pretty straightforward problem.

[NiftyNev]

Personally, I wouldn't buy a surf from a 'very good' mechanic who was unable to diagnose what is, in the scheme of things, a pretty straightforward problem.

Yeah you have to wonder don't you. It may be something simple but may also be a very dodgy head replacement.

Nev

[TonyN]

They need to test the coolant for exhaust gases to prove its a gasket head issues, or just a cooling problem with the pump/rad/cap.

[BUSHWHACKER]

It doesn't matter now anyway, I think he's gone back to the future.