Could the water pump put air into the cooling system? I have a 93' Taurus. Air is getting into the cooling system and forcing just enough of the coolant into the overflow tank so that the heater doesn't work. First I thought head gasket, but the engine still runs smooth, there's no water in the oil, and water doesn't seem to be getting into the cylinders. I hooked at tube to the cooling system and put the end in a jar of water. Bubbles come out at irregular intervals; sometimes fast and furious and sometimes not at all. It seems to depend on the engine temp. (or along the process of heating up) Thanks, Jeff