** Up date**
I noticed this happens during idle... Long stop lights sittng in a parking lot ect. Could this be an effect of lack of psi in the system? I.E. head gaskets about to go or maybe just a bad degess cap. I have noticed minor puking out he cap.
Lately I've notice that I don't any hot air comeing out of any of the vents
It doesn't matter if I have the set on defrost, vent or floor. I can feel the air come out but its not hot. And it happens very random, I'll have hot air then boom it almost cold. Even though its 43* outside its comfortable inside the cab. I know it takes longe for your trucks to get warm, But I drive 14 miles to work and sometimes still not hot.
Before I start tearing into my dash looking for a vacume leak or the flapper of the heater core, does anybody have any thoughts?