I presently own a 1983 300td. Love the car. Now that it is getting colder here in the east, I'm back to using the heat in the mornings. The car warms up rather quickly and starts to blow nice warm/hot air. I can drive all around town under 50 mph and still get the heat. When I get onto the highway and go over 50mph the heat stops. Cold air blows. When I get back inot town and drive below 50, the heat is back... Go figure?

any help would be apreciated.

thanks,
Andrew