Originally Posted by ah-kay

I am no OM603 expert but know enough to be dangerous. My experience are:

1) don't throw new parts at it unless you know the root cause. It may mask the symptoms.

2) make sure coolant is ok. No air in cooling system. Run car to temperature or whatever you feel comfortable with but making sure the system is pressurized. Then do a hose squeeze test next morning. The hose should be soft and NO pressure in system. Assuming the system is air tight. If it is still pressurized then the head likely is breached.

3) gas in coolant test: cold engine first. Fill radiator to the brim or close to it. Start engine and check coolant level. If level rises and overflow or bubbles coming out then head is likely breached.

Good luck.