My 2003 Aerio is taken careful care. It is treated like a family member.
I live in Puerto Rico, tropical, where we have a 12 month summer weather. No cold weather seasons.
Following the owner's manual instructions the coolant level at the water reservoir was constantly checked.
It had this problem: The water reservoir is filled up to the max line.
When driven it would over fill. And the radiator lost water.
After that I checked radiator and constantly added coolant.
the Radiator cap was changed.
Mechanic and radiator people said it was no problem.
Last week the rad exploted breaking the taps.
It was replaced with a new one with new hoses.
Air flow meter, crankshaft sensor were checked, mechanic said they are ok.
Water pump broke and was replaced with a new one.
Computer was replaced with a used one.
The older computer got wet from rain water from windshield filtering. This was fixed with urethane rubber and top had fixing, soldering and repainting job done on it.
The radiator has the same problem, reservoir keeps overflowing and coolant has to be added to the radiator.
No coolant is leaked to the floor.
Could it be the thermostat, or what? ?