Cracked head actual symptoms

[Daan]

Hi there,

Recently had an issue with my m20b25, gets hot quickly and pushes a lot of coolant out. Just removed the head and the gasket doesnt look obviously blown anywhere, and the head looks like it has previously cracked in the usual place and been welded.

Just wondering if when they crack (in the usual place) the symptoms are just oil/coolant mixing, or if combustion gasses get involved aswel and pressurize the coolant?

I had no mixing of coolant and oil, just pressurized coolant.

Thanks in advance, Dan.

[Brianmoooore]

Common cause of coolant pressurising with a M20B25 is corrosion around the crescent shaped coolant holes on the head face. These are very close to the gasket fire rings, and if the corrosion encroaches under these, gasses will get into the coolant.
Head can crack around an exhaust valve seat as well, which can also put pressure into the coolant.