If it's doing something this winter that is DIFFERENT than previous winters with the same parts, then yes, it's possible your t'stat may be not be closing all the way when it's trying to modulate engine temp. The common symptoms for that are lower engine temps, and heaters that take longer to start working, and don't produce as much warm air. OH, and gas mileage may suffer along with automatic tranny's that tend to hold the lower gears longer before they shift -- just like when the car is running cold. Because it's running cold longer.