Peugeot 306 dt pressurising its coolant

[anto]

I have a 306 turbo diesel that is pressurising its coolant.
Does not overheat.
Slight brown film in the header tank after 4/5 miles of driving.
I have checked;

Thermostat - opens as should
new rad - pressure burst the old one
new rad cap - no change
i have taken the head off and as far as i can see the gasket is intact, no breaks in the gasket between cylinder and water ways which was what i had expected
No obvious signs of a crack in the head.

Any ideas folks?

Thanks,

Anton

[anto]

Anybody?

[darrenjlobb]

Have you had the head pressure tested yet mate?

Its probably warps...really common on these motors...

Ive had field cars that simply have NO compresssion. took them apart, look 100% fine, replace head, and away they go again...

[anto]

Got it tested darren, came out fine.
It wasnt warped either, so must have been the gasket.
It was corroded near the water channels so perhaps it was enough to build pressure in the coolant.

Im glad i did it anyway, the head and valves were badly coked up so ive cleaned both and il grind the valves in so it should be a freer flowing head when i rebuild it.
Ive new stem seals as well to go on.

It will eliminate the head if it doesnt work.

Could possibly be a cracked block? How likley is that?