Running Your A/C vs Driving With the Windows Down: What’s Better for Fuel?

It’s hot outside. Your vehicle can be the perfect escape from the summer heat.

There’s an age old debate: is it more fuel efficient to drive with the windows down, or to run your vehicle’s air conditioning.

The truth is; neither option is going to be good for you fuel mileage.

Let’s start by having the windows down. Driving with your windows down increase the drag your vehicle’s facing, therefore slowing it down. You compensate for this decrease in speed and increase in drag by stepping on the gas pedal more, thus using more fuel.

Running your vehicle’s A/C will not influence your vehicle’s drag. Your air conditioner is powered by the engine. Keeping your car cool with the air conditioner will result in the engine working harder; therefore you will use more fuel. The higher to crank the air, the more fuel your car burns.

So, we’ve established that both cooling options are going make you spend more at the pump. But we also know that driving on a roasting summer day with neither is not a real option for anyone. So, let’s figure out what option is more fuel efficient. Luckily, General Motors already did the work for us.

Back in 2004, GM ran multiple experiments to test which method burned more fuel. Researchers used a wind tunnel and they tested various real-life driving conditions. They drove an SUV at speeds of 50kph, 80kph and 110kph. All tests were conducted at a typical summertime temperature of 30C.

We’ve included two charts below that break down the results of the study. It concludes that running a vehicle with AC (the blue line) will require more gasoline than simply driving with the windows down (green line). If you really want to save money, driving with the windows up and no air conditioning is the most economical (and more uncomfortable) ride.

The results became even clearer when an SUV with an 8.1-litre V8 engine was tested on the track.

Fuel Consumption SUV Fuel Consumption Sedan

Jamie Hyneman and Adam Savage from TV’s Myth Busters also conducted a similar experiment. Both hosts drove identical SUVs, both had exactly five gallons of fuel and both drove on the same Northern California race track. Jamie cracked up the AC, while Adam rolled the windows down and they drove until they ran out of fuel. Jamie’s air conditioned vehicle ran out of fuel first, Adam was able to drive for an additional 24 km in his SUV with the windows down.

Both studies clearly prove that your air conditioner will burn more fuel than driving with the windows down. Now that you have the information you can determine how to stay cool this summer!