I have one of them there fancy pants air conditioning control systems that ain't got none of them there **** dohickies. Well, purely in the interest of science I decide to turn of the a/c and and use the vent setting to see if my gas mileage would go up. Bear in mind, I live down yander in the swaps of S. Florida, so I have never, and I repeat, never used the heat in this here truck once. So I wait and sees what happens..... Lo, and behold, there was some very toasty air blowing from them there vent thingys. Now this leads me to believe that I might just be having some nice warm radiator juice bleeding into the heater core, causing my vents to blow warm. What do ya'll think?

 

Cute.

Coolant always flows though the heater core.

Check the operation of your blend door.

 

you may also be getting a lot of heated air from off the engine and hood livin'down thar.

 

Ya don't say! Well, them Detroit boys done did it now.

 

Except on Max A/C with the temperature turned all the way to cool. In this case, vacuum closes the heater control valve (if equipped) and stops flow to the heater core.