It’s probably not a surprise that using your car’s air conditioning (A/C) is the main contributor to reduced fuel economy in hot weather. How great of an impact it has depends on a number of factors such as the outside temperature, humidity, and intensity of the sun. During hot summers, air conditioning use can reduce a conventional vehicle’s fuel economy by more than 25 percent.
Driving with your windows down can also reduce fuel economy. Open windows increase aerodynamic drag (wind resistance), so your vehicle requires more energy to push through the air. This effect is quite small at low speeds but increases at highway speeds.
To improve fuel economy in hot weather:
- Park in the shade or use a sunshade so that the cabin doesn’t get as hot.
- Drive with the windows open for a short time before using your A/C. Letting hot air out of the cabin first will put less demand on the system and help your vehicle cool faster.
- Don’t idle with the A/C running before driving. Turn the A/C on after you begin to drive or after briefly airing out the cabin. Most A/C systems will cool the vehicle faster while driving.
By Fred Blood
Air Quality Program Specialist
Capital Area Council of Governments