While driving, i get decent heat but i feel like it should be much better. At idle, i get luke warm air. When its really cold out, say anything in the teens and lower, at idle i get cold air, and driving i get luke warm... And thats with the heat selection at 84, doesnt change no matter where it is... What gives? Im still new to mercedes, but i know this cant be right. Coolant is all topped off, but i honestly dont know what else to check. Ive read that these cars have a heater valve, could that be part of the problem? And its a diesel model, if that makes any difference.. thanks!