I have puzzleing problem. I can start and drive my car 12 miles on the highway, and the temp gauge doesn't budge, and the heater blows our air that is barely warm. However, if I stop at a light, the temp gauge starts to rise and the air gets warmers. Alas, as soon as I start moving again, the temp gauge drops and the air gets less warm. Any ideas? It's starting to get really cold here.