here on the cold Canadian prairies - we have winter fronts with flaps. It is going to be below -15C close flaps - Daytime temp over -15C - open flaps - and always keep an eye on your temp guage.
Sounds a little strange that your guage will go below 80C at only -10C on the highway. Have your thermostat checked before resorting to a winter front. If your engine is not at aperating temp - excessive wear, poor gas mileage and other problems will exist. If you read higher up this thread you will see that the thermostat BEGINS to open at 80 to 87C.-engine is not holding temp - check your thermostat