Why does the engine temperature go down when driving in the winter?

It could be a stuck open thermostat that not allowing the temp to get up to normal operating temp be sure to check the raditor cap Maybe I am tired or just missing something, but if it is cold, and your moving, it raises the wind chill factor up. Or more cold air is hitting the radiator and cooling it down. It makes sense. thats common sense..something hot meets something cold, it cools down.. e.g. hot water in snow.. an ice pop in the sun.. If the thermostat is working properly, the temperature of the water in the engine block will rise only to the rating of the thermostat. Once the coolant water goes to the heater core or radiator, the cold air will be very efficient in removing heat from the coolant. If there is no antifreeze in the coolant, water can freeze in the radiator, blocking proper flow and causing the engine to overheat.