AC or Windows Down: Secrets to Better Fuel Economy

Summer is peak travel season for most Americans. Those hoping to spend less on fuel and more on fun can find ways to stretch their travel budgets with better vehicle care and use. One hotly (pun intended) debated topic during summer driving season is whether it is more fuel efficient to use the air conditioner (AC) or roll down the windows and catch the breeze to stay cool. To settle the AC versus windows question, researchers at Oak Ridge National Laboratory in Tennessee compared the performance of a Ford Explorer and a Toyota Corolla. It's probably no surprise that fuel consumption was the lowest when AC was off and the windows were up. But that's not a great option on a 95-degree day. When driving at speeds slower than 75 mph, researchers found it was more efficient to roll down the windows. At speeds faster than 75 mph, it was more efficient to run the AC in the Corolla, but not the Explorer, likely because the larger cabin was harder to cool. Edmunds.com experts found similar results with a Toyota Tundra, which got almost ten percent better gas mileage at 65 mph with the windows down and AC off. In Consumer Reports tests with a Honda Accord, using air conditioning while driving at 65 mph reduced gas mileage by more than 3 mpg, while the effect of opening the windows at 65 mph was not measurable. So deciding whether to choose AC or open windows depends on driving speed, wind speed, terrain, vehicle size and aerodynamics. Thankfully, other ways to improve fuel efficiency are less complicated. Good vehicle maintenance is the best way to improve fuel economy, says Andrew Hamilton, technical services and quality manager for Cenex brand lubricants. "To maintain your vehicle's top fuel efficiency, perform regular maintenance, including oil changes and replacing the air filter and spark plugs," says Hamilton. Use the manufacturer recommended engine oil to get the most from your engine. "Using the wrong oil viscosity can reduce fuel efficiency by five to ten percent," says Hamilton. "Use the correct oil grade and choose an engine oil that contains friction modifiers, such as a full-synthetic oil like Cenex Maxtron." Finally, don't forget tire care. The U.S. Department of Energy reports that 1.25 billion gallons of gas are wasted every year by driving on underinflated tires. "Properly inflated tires last longer, reduce braking distance and improve fuel efficiency," says Hamilton. The inflation guidelines can be found in the vehicle's owner's manual or on the driver's side door.