12R motor boiling out coolant

[Centretek]

I have a 1976 HiAce Commuter with a 12R motor.
Recently, it dropped a valve head into #4cylinder. Destroyed the piston and the head but bore had only slight scratch.
Fitted second hand head and piston. Compression test shows all cylinders within 5 psi of nominal, BUT, runs quite warm and blows out coolant as steam a minute or so after engine turned off.
No appreciable bubbles in coolant, fuel /air mix OK,no surging of coolant when revved and no water in oil or vice versa.
Any ideas?

[turbo4agte]

Blows coolant out of what? radiator cap? overflow bottle?

Did you try doing a coolant system pressure test?

[allencr]

Even though the water temp doesn't seem to be much higher, that temp is just the average of what's coming out of the head. There is something in there that is at a MUCH higher temp then usual, and it boils over when the coolant flow stops.

A clogged passageway in the head is very rare, so I think the radiator is clogged & your gauge isn't showing how hot it really is.

[blaze86vic]

leaking head gasket. Small leak from the combustion chamber to a coolant passage, Does it bubble like this? If so then head gasket.

http://www.youtube.com/watch?v=NMCfTAjMJBA