Dear Volvo from Heck,

Hope you're well and stay so!!! I quite agree. I long ago - in this post's history - suggested to metallo that he have the coolant tested to see if exhaust gases were present. Were exhaust gases found in the coolant, that would instantly inculpate the head gasket.

Even on a turbo-equipped engine, I doubt there's a way for the exhaust gases that drive the turbo to get into the turbo's cooling system. A coolant leak in a turbo would result in coolant loss, but not the extreme cooling system over-pressure metallo reported.

I suppose a water pump could seize-up, if a failing bearing were denied attention. That, though would first register on the temp gauge, in the form of the indicator needle to the right of center.

Yours faithfully,

Spook