Will you get worse gas mileage in cars when the A/C is on or when the windows are open?

Question

On newer cars - made in 2000 or later.

highway and town

Answer 1

Yes and yes.

The A/C unit on your car will usually be powered by a drive belt from your engine's crankshaft. This basically means your air conditioning drains a small amount of power from the engine. Therefore more power is required to achieve the same performance and more petrol is then consumed.

When you have your windows open, you are affecting the aerodynamic flow around the car. This doesn't really have an affect around town. But when on the highway, once you start exceeding speeds of 60mph(96km/h) aerodynamics begin to have a greater affect on the cars performance. It will cause disturbed air flow and drag, thus you will need more power to achieve the same performance as if the windows were closed. This will mean more petrol is consumed.

So, A/C is a luxury but it will cost you petrol. And its fine opening the windows but once your out on the highway you should close them. If it is hot on the highway, then use the A/C. Less petrol will be consumed than having the window fully open at over 60mph(96km/h).

Answer 2

Well, with the windows open, air gets trapped inside the back of the car creating drag.The a/c doesn't run all the time, only enough to cool.  So my guess would be that there is not too much difference between the two.

Answer 3

You will absolutely get less mileage in a car with the A/C on. It takes power away from the car.