What’s More Efficient: Car A/C Or Rolling Down The Windows? We Have The Numbers

It’s summer time again, and the eternal question arises once more; is it more efficient to use your car’s A/C or simply roll down the windows?

Before going into the calculations, it has to be said that neither will make your car “more efficient” since opening the windows increases the drag coefficient, while running the A/C puts extra load on the engine, worsening your car’s mpg numbers.

Clearing the obvious out, General Motors and SAE collaborated back in 2004 to find out a definitive answer to the question. The results were published in the report called, “Effect [sic] of Windows Down on Vehicle Fuel Economy as compared to AC load.”

The experiment consisted of using a wind tunnel and running a sedan SUV’s sedan, with a 4.6-liter V8 engine, at speeds of 31 mph, 50 mph, and 68 mph, under 86 degree F weather.

The results are inserted below, with the blue line depicting the A/C option and clearly showing this choice consumes more gallons of gas per mile than driving with your windows rolled down, represented by the green line.

The red line shows how much money you can save with no A/C and the windows rolled up, which is quite a bit of difference!


A similar Here’s how the numbers work out for an SUV, with an 8.1-liter V8 engine:


You can also watch Discovery Channel’s “Mythbusters” episode on this, who also found that opening windows is the most efficient way to go!

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