Coolant issue (non-bump vehicle)

[flyboy71]

Ok this isnt a bump issue but its driving me insane. On our '02 Taurus, once in a while, only when it feels like it, the coolant reservoir overflows when the engine is either at idle or after its shut off. You can watch the level creep slowly to the top and cook out around the cap. It doesnt do this all the time, just once in a while and Im not sure if its exactly worse on hot days or not. I pulled the water pump thinking it wasnt circulating enough and overheating and it was fine. Changed the thermo. Fushed the system and refilled with the correct mix. Even the reservoir was replaced because the old one had a crack in it and was leaking. The leak is gone, but the boil over is new. As far as I know the cap is holding the pressure correct in the system. Have any of you had this problem on newer cars with the closed system and coolant reservoir?

[fordman]

how did you flush it? what did you flush it with. does the fan kick on sometimes after the car is shut off? some of them are suppose to do that. if it isnt maybe the sensor to turn it on is bad or something in that circut is bad.

[flyboy71]

I flushed it with the garden hose when I had everything off checking the water pump so the engine, rad, heater core everything had water flushing through it. Yeah the fan runs as it should and the temp never goes above half scale. A few folks said maybe the head gasket is leaking into the coolant system and overheating it. There is no white smoke at startup though and no creamy white oil so if its leaking its not leaking the other direction.

[fordman]

can you see inside of the radiator and see any deposits on the tubes or around the tubes? is there any bubles in the water when the car is running? that woudl be caused by combustion gases getting into the water jackets. but might not get into the oil. and the water might not be getting into the cylinders.

[flyboy71]

The Taurus doesnt have access to the radiator to look in. I had noticed bubbles awhile back in the coolant reservoir but not the past few times. Thats what prompted me to think it was gases leaking in. I dont smell any fumes though when I take the cap off it just smells like clean antifreeze. I would think it should boil over all the time unless the leak comes and goes. The car is hitting 160k+ miles so its nearing the end of its life I guess.