I recently replaced a bad temperature sensor that was leaking quite a bit of coolant. No coolant leak now, but the "I'm hot" light came on during a cross country trip. Checked every time we got fuel and no coolant was lost. A couple of days after returning home, I checked and the expansion tank was almost empty. I don't have any puddles anywhere. I have a bad feeling that I'm about to lose a head gasket because I can smell hot coolant even though the car is not overheating and the coolant loss is now minimal. The thermostat housing is not leaking, but I fear it may be stuck open, so I'm ordering another (the one I first ordered would not fit due to the throttle body and the position of the bleeder on the housing). The pipe does not leak and the seal is tight. I will probably go ahead and replace the water pump while I'm at it. Weird thing... I don't smell the burnt coolant in the vents and the cooling fan does come on...full strength after 15 minutes or so. Has anyone found a decent head gasket sealer that can fix an early problem?