Is it true that a car uses less petrol with the air conditioning on and windows closed...?

Question

...than with the windows open and the air conditioning off?

Answer 1

The answer is yes. Automobiles today are designed in a wind tunnel using mock up designs with the windows CLOSED. At the proving grounds, we have noticed that fuel economy drops around 5% with the windows open compared to windows closed and the air on. With the windows open, the dynamics of the car change, and the airstream actually blows into the car and pressurizes the cabin, and acts as a sort of parashute.

Answer 2

Yes, the open windows  allow air into the car which has a braking effect. try dragging an open bag through the air.

Answer 3

Myth Busters did an episode on that exact topic.  I saw the episode forever a go, but I forget the outcome.  I'm sure you can find it on the web.

Answer 4

Only on the hwy.

For best MPG:

HWY speed - AC on and window up.

STREET speed - AC off and window down.

The BEST - AC OFF and window UP.

I was out today and was just going for a short drive. The above was kind of moot because it was so hot I could not drive with the AC off (which I normally prefer - regardless of cost).

Good Luck...