kirkcor

I appreciate all the replies, they have been very helpful. I do not see any evidence of bubbling from either the radiator or the overflow tank. I also do not see any coolant leaks when it is running or where it was parked overnight. I guess it's down to the radiator or water pump, but wouldn't there be a noticeable noise if the water pump failed?

I'll check for the bubbles in the morning and check the flow as you suggested. The fan does come on when it comes up to normal temp. Is it still possible to have a blown head gasket if I am getting compression readings of 170PSI on all four cylinders?

My 1990 Legacy LS wagon with 176K miles has recently started overheating. I changed the thermostat, flushed the radiator, bled the cooling system and ran a compression check (all cylinders have a PSI right around 170). It doesn't overheat when idling, but overheats (close to red) within a few minutes after driving. It seems to start overheating once I am above 35 MPH. The water pump isn't making any noise and I don't see a coolant leak and there is no coolant in the oil. I have only had the car for a couple years and don't have any kind of maintenance history on it. I am out of ideas and any suggestion would be welcome.