Cracked block?

[Turbo-Brown]

This is for an M20B25

The symptoms are that it would overheat if you let it, the top hose stays cold, the heater doesn't work and it pressurizes the coolant.

It's got a known good 'head on it and has a brand new head gasket, water pump and viscous coupling.

It starts fine from cold, but if you switch it off and then go to re-start, it struggles to compress what's presumably water in one of the cylinders, then spins over and fires.

Sound terminal to anyone else?

[Brianmoooore]

After its been stopped, take the plugs out and spin it over. If you get a face full of water from one plug hole, then your water in cylinder theory is confirmed.
It's not impossible for a block to crack, or even for a duff casting to finally go porous, but it would be very unusual to say the least.
How are you so certain this new head is good?

[Turbo-Brown]

The head came off another another car which I had and ran around in for a bit. Not a cast iron guarantee I know, but the symptoms the car I've been trying to fix are exactly the same with this different head and gasket.

Will whip the plugs out and give it a spin, not hopeful this one can be salvaged though

[DanThe]

Ive had an M50 block with a crack in it, was from the head bolt hole over to the water jacket. Crack into the cylinder would show itself very quickly though I expect and you would be seeing coolant in the oil.