[AcampoDave]

I don't get it. If a thermostat were functioning properly then (apart from sub zero temps), it should run at the rated temp. The thing closes up, obstructs the flow, and the block heats up. Is your heater's water flow path bypassing the thermostat somehow? Have you played around with the hoses yet? Sorry pulling the Mr. Gasket didn't help, but it seems there is still a solution. Chevy made their trucks to operate properly in cold weather.