In the summer you ran your a/c. When the a/c is running the cooling fans should
run at low speed. This was apparently enough to keep you satisfied with the car's
temp. When you did not use the a/c, your fans were not on low speed. And
apparently, the temperature sensor did not tell the fans to come on. Could be the
water is low so the temp sensor did not figure out the car was hot. Could be the
temp sensor is bad. Obviously refill the radiator and bleed it first. If more is
needed check the sensor. The sensor is located near where the upper radiator
house goes into the top of the engine and near the thermostat or under and at the
front side of the throttle body.