Driving with Air Conditioning on or Windows Open, Which Saves Gas?

On a warm day a driver has the option of driving with the windows open or with the air conditioning running. Many people think that leaving the windows open is more gasoline efficient. Others feel that wind drag eats up more gasoline that running the air conditioning with the windows closed. I finally had this question answered by WTOP All News Radio on May 25th 2008.

WTOP reporters tried it both ways over a long distance and it turned out there was virtually no difference in gas mileage either way. The wind drag produced by opening windows causes about as much decrease in gas mileage as using air conditioning. There are a few variables however. If you are in heavy stop and go or very slow traffic, it is more efficient to open your windows. Under this circumstance you also decrease the chances of your engine over heating on a hot day. At slow speed the air flow drag is minimized.

If you have hay fever or other allergies related to unfiltered fresh air, you might want to use your air conditioning rather than leaving you windows open. You will not get better mileage, but you will feel a lot better for the same energy usage.

WTOP gave several other tips for getting better mileage. First and most importantly, make sure your tires are inflated fully. An underinflated tire or tires can cause a major drop in your miles per gallon. Second, Drive your car, van or truck at between 30 Miles Per Hour (MPH) and 60 MPH. Increasing your speed to 65 MPH or more on a highway lowers your gas efficiency dramatically. You also may be increasing your chance to get a traffic citation with a hefty fine with several points on your license as well. Third, accelerate slowly and break as little as possible. Fourth, do not let you vehicle idle for over a minute. It is better to turn your car off if you expect to idle longer and there is no safety danger.

Additional gas saving ideas are car pooling and keeping the weight in your car to a minimum. Take that sand bag that you would use for snow traction out of your trunk during the warmer months. Keep your car clean and free of dust. A very dirty car can decrease mileage because of air friction's breaking effect. Use the minimum grade gasoline your car specifies in your automobile manual. Additional octane will not increase mileage. In addition lower grades usually have more detergent to keep you engine running efficiently.

Happy driving and may the cost be with you.