Radiator is clean and the thermostat has been replaced. It just passed smog test and runs great. It overheats slowly and pushes the coolant into the overflow tank.

Could this be the head gasket. 116K miles.

Are you sure your radiator is completely clean?. Have you had it rodded?. If not, take it to rad shop.

Roy

I had the same problem, had the rad flushed, replaced the fan clutch...no help. Then I replaced the rad cap and it's been good since.

Good advice Roy, better get that radiator rodded out. Radiator man that repaired mine said those radiators get clogged easy. Made a world of difference on mine.