Fuel Economy in Hot Weather
Hot weather can actually increase your fuel economy. Your engine warms up to an efficient temperature faster; summer grades of gasoline can have slightly more energy; and warm air causes less aerodynamic drag than cold air.
However, keeping passengers comfortable in hot weather by rolling down the windows or using the air conditioning (AC) can reduce fuel economy.
Running your car's air conditioning is the main contributor to reduced fuel economy in hot weather. Its effect depends on a number of factors, such as the outside temperature, humidity, and intensity of the sun. Under very hot conditions, AC use can reduce a conventional vehicle's fuel economy by more than 25%, particularly on short trips.1,2,3 The AC's effect on hybrids, plug-in hybrids, and electric vehicles (EVs) can be even larger on a percentage basis.2
Driving with your windows down can also reduce fuel economy. Open windows increase aerodynamic drag (wind resistance), making your vehicle use more energy to push through the air. This effect is quite small at low speeds but increases at highway speeds.1,4
What can I do to improve my fuel economy in hot weather?
- Roll the windows down at lower speeds; use the AC at highway speeds.
- Don't use the AC more than needed or set the temperature lower than needed.
- 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 the AC. Letting hot air out of the cabin first will put less demand on the AC and help your vehicle cool faster.
- Don't idle with the AC running before driving. Turn the AC on after you begin to drive or after airing out the cabin briefly. Most AC systems will cool the vehicle faster while driving.
- Read your owner's manual. Most manuals explain how the AC system controls work and how to best use and maintain the AC system.5
- For plug-in hybrids and electric vehicles, pre-cooling the cabin while plugged into the charger can extend your vehicle's range. Also, using a warmer temperature setting for the AC will use less battery power.
- Huff S.P., B.H. West, and J.F. Thomas. 2013. Effects of Air Conditioner Use on Real-World Fuel Economy. SAE paper 2013-01-0551 (doi: 10.4271/2013-01-0551). SAE 2013 World Congress, Detroit, Michigan, April 2013.
- Lohse-Busch, H., M. Duoba, E. Rask, K. Stutenberg, V. Gowri, L. Slezak, and D. Anderson. 2013. Ambient Temperature (20°F, 72°F and 95°F) Impact on Fuel and Energy Consumption for Several Conventional Vehicles, Hybrid and Plug-In Hybrid Electric Vehicles and Battery Electric Vehicle. SAE Technical Paper 2013-01-1462 (doi:10.4271/2013-01-1462).
- Thomas, J.F., S.P. Huff, L.G. Moore, and B.H. West. 2016. Measurement of Vehicle Air Conditioning Pull-Down Period. ORNL/TM-2016/275. Oak Ridge National Laboratory, Oak Ridge, Tennessee.
- Thomas, J.F., S.P. Huff, and B.H. West. 2014. Fuel Economy and Emissions Effects of Low Tire Pressure, Open Windows, Roof Top and Hitch-Mounted Cargo, and Trailer. SAE Int. J. Passeng. Cars - Mech. Syst. 7(2):2014 (doi:10.4271/2014-01-1614).
- Furse, D., S. Park, L. Foster, and S. Kim. 2014. Real World Customer Usage of the Hyundai Genesis Climate Control System in the USA. SAE Technical Paper 2014-01-0685 (doi:10.4271/2014-01-0685).