Dear Metallo,

You described:
- Before starting the engine, the antifreeze was at min. level, cold engine.
- I removed the expansion tank cap, turned the engine on.
- Slowly I have seen the antifreeze level going up, no bubbles.
- Soon after the temperature needle reached the middle, the antifreeze overflew from the tank, but no bubbles.
- I turned the engine off

Same would happen if you have a jammed/stuck thermostat. But that didn't explain the rough start.

In normal engine if you start the car with coolant level at min (expansion tank cap off), the level would raise until about max, when the radiator fan kicks in, the level would back down back to above min. There wouldn't be any overflow. Of course no bubbles there.

You might have 2 issues at same time - marginally leaking headgasket and stuck thermostat. Lets see what the Volvo shop says.

I'd say marginally leaking as there is no bubbles in your coolant. The small headgasket leak had closed up during engine running as the metal expands when hot. But during engine cooldown the leaking gap would open again and some coolant would seep into the cylinders making a rough start coming morning.


Amarin