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9 Fuel Efficiency Myths Debunked

by hlclark on April 14, 2010

As the price of fuel continues to rise, we’re all looking for ways to increase our fuel mileage. Lots of theories abound about how exactly to do that, but many of them simply aren’t true. Here is the truth about some common fuel economy myths.

  1. Leaving your windows down creates an aerodynamic drag that cuts your fuel efficiency.
    And closely related…
    Running the air conditioning causes fuel efficiency to plummet.

    We’ve all heard both of these warnings – so which one is true? Well, driving with your windows open does increase your car’s aerodynamic drag, but it hasn’t been found to have a measurable effect on fuel economy.

    And as for running the air conditioner? Studies conducted by Consumer Reports and found that while running your vehicle’s air conditioning causes your engine to work harder, it only reduces fuel economy by about 1 mpg at highway speeds. So really, you’re not losing that much. However, if you’re just running errands around town, you may save some gas by keeping the A/C turned off and the windows rolled down.

    Experts at both Consumer Reports and found that fuel mileage is roughly the same whether the windows or down or the air conditioning is on. Of course, that can vary slightly from car to car, since each make and model is different.

  2. Frequently starting up and turning off your engine burns through fuel quickly.
    This myth most likely got its start in the days when cars had carburetors. However, thanks to today’s fuel-injection technology, drivers actually save gas by turning off their engine rather than letting it idle unnecessarily for long periods of time.
  3. Fill your tank in the morning while fuel is cold.

    This myth most likely became popular fluids are more dense at lower temperatures. Given that bit of science, a gallon of cold gas actually has more gas molecules than a gallon of warmer gas.

    But according to Consumer Reports, the temperature of gasoline as it comes out of the nozzle varies little during the course of the day. So really there’s not really much benefit to filling up your tank early in the day.

  4. Change your air filter.
    It’s important to keep up with routine vehicle maintenance, but having a dirty air filter isn’t going to hurt your fuel economy – but it will almost negligibly decrease engine power. Today’s engines have computerized sensors that automatically adjust the fuel-air mixture, so clogged air filters don’t factor into gas consumption.
  5. Pump up your tires.
    There are several reasons to make sure your tires are properly inflated. If your tires are under-inflated, you may experience bad handling or even a crash, plus your tires will wear out faster. An equally important, under-inflated tires reduce will reduce your fuel efficiency.

    However, you should never over-inflate your tires. You may get slightly better fuel economy because there will be less tread touching the road, which reduces friction. But that also means less grip for braking and turning, which increases your chances for an accident.

  6. Use premium fuel.
    Many drivers believe that they must fill their tanks with premium gasoline because their vehicle owner’s manual recommends it. Most newer cars do just fine with regular fuel. Why? Because newer engines have sensors that detect what kind of gasoline you’re using and adjust spark plug timing accordingly. The result is no difference in fuel economy. However, if you notice your engine knocking, go back to using premium. It doesn’t happen often, but you should be aware of the possibility.
  7. Don’t waste your time shopping around for cheaper gas, since it’s not worth the extra fuel you’ll use trying to find it.
    Sometimes it does pay to shop around to find the cheapest gas prices – and you don’t have to drive around to do it. There are many resources online, such as, that let you search your area for the lowest-priced fuel.
  8. 4. Keep your speed below 55 mph to get the best gas mileage.
    According to the U.S. Department of Energy (DOE), fuel efficiency doesn’t start to drop until you reach speeds higher than 60 mpg, and it’s mostly due to wind resistance and tire rolling resistance. Even then, how smoothly you drive makes a greater difference on gas mileage than your speed does. And once your car is up to speed, it really doesn’t take much energy to keep it going.
  9. If you want better gas mileage, drive a car with a manual transmission.
    While that may have been true in the past, newer automatic transmissions can get the same highway mileage – or even better – as a manual transmission, especially at highway speeds. New automatic transmissions even have an ‘overdrive’ gear that reduces engine RPMs at higher speeds.
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