I have a 93 Ford Probe. It is overheating and we have replaced the radiator, water pump belt, the cap twice, thermostat 3 times top hose and cleared the overflow hose that was blocked. After replacing the radiator and thermostat the car worked fine for several months then started to overheat when I turned the heater on. I don't have very good heat most of the time especially when I am going down a mountain. I noticed some kind of thick residue in the radiator and had it flushed. It still overheats. As far as we can tell the water pump is fine and there are no leaks in the system. No indication of blown head gasket or of a bad heater core. Could it be just a sensor gone bad??? Please help it's driving me crazy!!!!!