Mine very much is dependent on the air flow direction setting, outside ambient temperature, how hard the engine is working and more importantly the fan speed. It does take upto 5 miles to get it blowing very hot air if on fan speed 1. I never use auto. That said once warmed up it is consistent with the warm it is providing.One thing I have noticed is the heating isn't very good unless it's on the auto mode , is this a known issue ?