Department of Energy's Question of the Month
Question of the Month: How can I improve my gas mileage while driving this summer?
Answer: Whether you are taking a summer road trip or just running errands around town, there are things you can do to improve your fuel economy and save money on fuel in the summertime.
You may notice an increase in your fuel economy as the weather gets warmer. This is because vehicle engines, transmissions and other components take less time to warm up and summer gasoline blends can have slightly more energy per gallon than winter blends. However, if you use your air conditioning (AC) a lot or drive with the windows down, you might actually see your fuel economy drop.
AC is the main contributor to reduced fuel economy in the summertime. In fact, using the AC can reduce a conventional vehicle’s fuel economy by as much as 25%, or even more if you are driving a plug-in electric vehicle (PEV). Driving with the windows down can also reduce fuel economy due to greater aerodynamic drag (wind resistance) on the vehicle. Though this has a small effect on fuel economy, aerodynamic drag is more apparent when driving at the highway speeds typical for road trips.
The following tips can help you use the AC more efficiently and therefore improve fuel economy in the summer:
- Read the owner’s manual for detailed information on how your vehicle’s AC system works and how to use it efficiently.
- Park your vehicle in shady areas or use a sunshade to keep the interior from getting too hot.
- Do not use the AC more than needed. If you need to use the AC, avoid using the “max” setting for extended periods.
- If you are driving at high speeds, use the AC instead of rolling down the windows. If the vehicle is too hot, you may lower the car windows to expel hot air for the first few minutes. Once the hot air has left the vehicle, switch to using the AC.
- Avoid excessive idling. Idling can use a quarter to half a gallon of fuel per hour, and more if the AC is on. Do not idle the vehicle to cool it down before a trip; most AC systems actually cool the vehicle faster while driving.
- PEV owners, pre-cool your vehicle with the AC while still plugged in. Since PEVs use battery power to provide AC, it can drain the vehicle’s batteries and reduce the vehicle’s overall range. If you need to use the AC to cool down your PEV, try to do so while the vehicle is still charging.
The following tips should be used year-round to improve fuel economy:
- Use cruise control while driving on highways to maintain a consistent speed and conserve fuel.
- Remove any unnecessary weight from the vehicle. Vehicles with heavier loads tend to have reduced fuel economy. An additional 100 pounds in your vehicle can reduce fuel economy by 1%.
- Avoid transporting cargo on the rooftop of the vehicle. Traveling with cargo on the roof increases wind resistance and can significantly lower your fuel economy. Rear-mounted cargo has a much smaller effect on fuel economy than rooftop cargo.
- Avoid aggressive driving. Aggressive driving (speeding, quick acceleration and heavy braking) can reduce fuel economy by as much as 33% at highway speeds and 5% at city speeds. This informational video shows real-world effects of aggressive driving on fuel economy: https://www.youtube.com/watch?v=4zWXwqqqHm0.
- Ensure your tires are properly inflated. Tires that are not inflated to the proper pressure can reduce fuel economy by 0.3% for every one pound per square inch (PSI) drop in pressure in all of the tires. Having your tires inflated to the proper pressure is also safer and can help tires last longer.
- Pay attention to the speed limit. Not only is this a safe practice, but gas mileage tends to decrease when driving at speeds above 50 miles per hour.
For more information on how to improve your fuel economy, please refer to the following FuelEconomy.gov websites:
- Fuel Economy in Hot Weather - http://www.fueleconomy.gov/feg/hotweather.shtml
- Gas Mileage Tips - http://www.fueleconomy.gov/feg/drive.shtml
- Keeping Your Vehicle in Shape - http://www.fueleconomy.gov/feg/maintain.jsp.
Clean Cities Technical Response Service Team
technicalresponse [at] icfi [dot] com