In that case, I would head to your mechanic and ask him to perform the "sniffer" test to check for a leaking head gasket. The test involves drawing air from the radiator through a glass tube filled with two chambers of dark blue liquid. If combustion gases are getting into the cooling system, the liquid will turn bright yellow.
Also check how hot the air is coming from the heater. If it is cool or just warm when the engine overheats, coolant flow is being disrupted. That could be due to an air pocket caused by the leaking head gasket, a loose belt driving the water pump, or a thermostat stuck closed. (Thermostats only open in response to hot liquid, not hot air).
Tuesday, March 16th, 2010 AT 8:46 PM