My wife's been driving my C70 all week - since the head gasket is failing in her 940 and the dang thing is on backorder... Loss is intermittent and minimal, but it's still a concern.

Anyway, she pulled up to the house in the c70 and the expansion tank cap suddenly started spewing hot coolant under the hood. No warning, no overheat, nothing ruptured. The OEM volvo expansion tank was quite "swollen" when I investigated, but all the hoses are intact - most are new Volvo OEM and Samco silicone. The entire cooling system is new - thanks to a failed head gasket in August. The only things that I didn't replace were the hardlines to the turbo and water pump itself.

Can't quite describe how much angst this new problem fills me with... Bit too much happening all at once...

Wife said there was no unusual road traffic nor was she stuck sitting in traffic for any length of time. It's pretty weird.

So, I let the car cool and noted that a fair amount of coolant was gone. Topped it off, and ran the car for a quite a while - seeing nothing. Had to top the coolant off again (not usual with a hot engine and lost coolant).

Ran two cycles of letting the car cool, checking the coolant level and then running the car at high revs for a while. I *carefully* watched the expansion tank for coolant loss or worse-bubbles and over-pressure in the coolant.

Saw nothing. I know that expansion tanks don't blow-off for no reason.

I've already replaced a head gasket on this car. I'm seeing none of those nightmarish symptoms so I'm hoping that I simply had a stuck thermostat...

Any chance that I'd be that lucky?

We're trading back tomorrow. my short commute is a good test for car with possible problems... short drive, close to home, etc...