My 1996 850 wagon, non turbo, has an unusual problem with coolant/steam coming out of the expansion tank cap after the temp reaches about 55%. It's fine up until that point and has happened twice in the last week - I've noticed that it seems to run a little hotter in stop and go traffic now than it did during the summer, and lots cooler on the highway. But it rarely gets to the 55% mark, and seems to hold there for a bit before it starts steaming out of the cap. As best I can tell, the expansion tank is not cracked, as it's not leaking when cold/low temp.

I have no CEL, and no apparent coolant leaking when it doesn't lose pressure, but I was not sure if the expanstion cap was bad, or if this was symptomatic of a thermostat stuck closed? Or perhaps there is another culprit for this?

Any help would be appreciated!

 

Sounds like the thermostat might be bad.

 

+1 on the thermostat. I would order a new one and replace it ASAP.