After replacing the power steering pump on my 2008 3.5l aura I took it for a test drive to check for leaks. Drove about 20 miles. When I opened the hood to check ps fluid I noticed coolant coming out of the pressure cap on the resivor. I checked the engine temperature gage and it was normal.
Replaced thermostat, ran and filled resivor many times until when cold level stayed normal.
Started car today for test drive, ran car for 10+ minutes all looked good. Drove 3 miles to fill gas tank. After filling I checked coolant and it was coming out of cap.
Started car, drove home, checked resivor with car running and it just a little above normal. Turned off car and the resivor rapidly filled and started dripping coolant.

Pressure cap maybe?

 

Do I understand correctly that the only times You have seen it expelling coolant through the reservoir cap are when the vehicle is not running?

Do the auxiliary cooling fans or fan run all the time when the car is running?

What brand of thermostat did you install?

 

In addition to what derf has asked you, I have to ask a couple of questions too. Are you running a 50/50 mix of antifreeze and distilled water? Have you checked the overflow hose for cracks or holes and have you tried replacing the reservoir cap? For some reason, something isn't sealing properly in the system. I'd rent a pressure tester and do a pressure test on it. I'm thinking it's either the reservoir cap or the reservoir itself. There may be a split in the plastic lip that the cap snaps onto.

 

Replaced pressure cap and everything seems to be working fine now.

 

Drive on