I know many say they work great but I had one on a 1979 300cd and all it did was heat the radiator. Looking at the thermostat the the heated water should come from the engine side to open the thermostat to allow water to flow through the engine, is that correct? The one I had did nothing but heat the radiator even plugged in all night. Too many people say they work for me to dispute that but I would like to know why mine didn't.