Well, we all know how there are two options with the ac, to circulate the air inside the car or use air from outside coming in. Clearly these are vents (can be open with the a/c off, prove to flow better with a window cracked, etc) that can be opened and closed.

This is where the question comes - Where is the opening for these airvents, where does the air physically enter the car?

My guess is the engine bay because when its cold outside and you have the vents open and the dial turned to hot, hot air comes through. With this in mind, I've tried to keep all vents open on full heat (w/all windows+sunroof open) on mountain drives. It may just be me but it feels as if its keeping my engine bay temps down (less heatsoak, fan not coming on after hard drives, etc) Could this be possible or is it in my imagination - Will keeping the outside airvents open + full heat really help air to circulate in the engine bay?

Keep in mind this is with the a/c fans off. If it does truly help circulate engine air would it be more beneficial to have the fan on pumping hot air out or leave the fan off and use the forced airflow from outside...

the heater system works by pumping hot coolant into the heater core (basically a small radiator) inside the passanger compartment and then fans blow it around.

so, yes, it would cool the engine, this is why when a car is overheating many people use this trick to make their car more driveable.

The air comes in via the vent at the base of the windshield - the little trench where the windshield wipers sprout. That's where the vent is on pretty much all cars. In the old days a lot of cars had a pop-up scoop there, but eventually everyone realized that's a high pressure area and needs no scoop.

If you lift the hood, you'll see there's weatherstrip to seal that area off from the hood. They are not going to direct under-hood air into the passenger compartment.

The heating/cooling action is as staticlag describes.

Ken

Thanks for the quick replies guys!