With gas prices rising again to a national average of $3.68 a gallon for regular according to AAA, the scientists at Oak Ridge National Laboratory have some advice on how to improve your MPG in hot-weather driving. The laboratory's Center for Transportation Analysis runs the government's fueleconomy.gov website for MPG rating information.
The most important mileage-boosting step you can take is to be smart when using your air conditioning. "Under very hot conditions, AC use can reduce a conventional vehicle's fuel economy by more than 25 percent," the scientists note. "The AC's effect on the fuel economy of hybrids, plug-in hybrids and all-electric vehicles can be even larger on a percentage basis."
The seemingly obvious idea of turning off your air conditioning and rolling down the windows is only partly effective -- open windows cause aerodynamic drag, thus using more gas. This effect hurts MPG especially at highway speeds, while the drag is much less when driving slowly.
Here are six steps you can take to boost MPG in hot weather:
- Set the air conditioning temperature as high as you can while still staying comfortable. Cooling more than you need just uses gas unnecessarily.
- Turn the air conditioner off and roll down the windows in slow city or suburban driving. Go back to the air conditioning at highway speeds.
- When starting out, drive with the windows down for a few minutes before turning on the air conditioning. Letting hot air out of the car lowers the burden on the air conditioning.
- Don't turn on the air conditioning while idling. The system will cool the car faster while you are driving
- With electric vehicles or plug-in hybrids, however, start the air conditioning while the car is still plugged in. This will help cut use of the battery for air conditioning and extend your range.
- Finally, park in the shade when you can or use a sunshade on the windshield so that your car doesn't heat up as much and thus won't need as much cooling.
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