4 gas-saving myths

Think you're stretching your gas dollars by killing the air conditioning or buying your gas on Wednesday? Think again.

By David Ellis, CNNMoney.com staff writer

NEW YORK (CNNMoney.com) -- Using a special additive or cutting off your A/C won't really cut your gasoline consumption. But myths like these run rampant in the minds of American drivers.

Right now, the price of gasoline is again setting record highs. The average price for a gallon of regular hit $3.087 Tuesday, the third record in a row.

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So before you attempt a half-baked scheme to stretch your gas dollars, here's a look at what's fact and what's fiction when it comes to fuel economy:

Nothing but gimmicks

There have been additives, special magnets and even a pill that has promised to improve a car's fuel efficiency by as much as 30 percent in some cases.

While the promise of stretching your gas dollars seems awfully lucrative, especially when they cost under $20, most of these products provide a negligible, if any, improvement in fuel efficiency, said Rik Paul, the automotive editor for the publication Consumer Reports.

Consumer Reports and the government's Environmental Protection Agency, have tested dozens of these products finding that none of them offer any significant improvement in fuel economy.

"With all the pressure car companies are under, if one of these inexpensive devices dramatically did improve fuel economy, they (automakers) would be all over it," said Paul.

Windows, air conditioning - does it matter?

There's the old saw that leaving your windows rolled down creates an aerodynamic drag on your car, cutting down on your fuel efficiency. And there's the notion that the fastest way to drain your gas tank is by running your air conditioning.

Neither one is exactly spot on.

Two separate studies conducted in 2005 by Consumer Reports and the automotive Web site Edmunds.com looked at how running the A/C and opening the windows affected the fuel economy of a sedan and an SUV traveling at highway speeds.

What they found was that running the air conditioner, while it did draw power from the vehicle's engine, only reduced each vehicle's fuel economy by about 1 mile per gallon. That's not a big difference unless you drive an already gas-hungry SUV.

The Consumer Reports' study revealed that, while opening the windows does increase the aerodynamic drag on a car, it does not have a measurable effect on the vehicle's fuel economy even at highway speeds.

Bottom line? Do what's most comfortable when driving on the highway since you're not going to save a whole lot of gas either way, say experts.

If you're driving around town on errands, you might save some gas rolling down the windows instead of using the A/C.

Don't wait until Wednesday

Some drivers insist the best time to buy gasoline is on a Wednesday, when pump prices have cooled from the weekend run-up when oil companies typically raise prices.

That's true to a point, says Tom Kloza, chief oil analyst at the Oil Price Information Service. Gas prices tend to be higher on the weekend, but there's no ideal day of the week to purchase your gas.

Geoff Sundstrom of the motorist organization AAA notes that gas prices fluctuate from day to day and are determined by gas station owners who look at a variety of factors including wholesale gasoline prices, competitors' prices and food and drink sales if they have an attached convenience store.

Drivers who want to bargain-hunt for inexpensive gas should instead check out Web sites like Gasbuddy.com, which allows consumers to find the cheapest gas in their area simply by entering their zip code.

Restart your engines

It's probably a myth that goes back to the days when cars were equipped with carburetors, but many drivers believe that starting up and turning off your car repeatedly is a fast way to drain your gas tank.

But because of modern fuel-injection technology, drivers actually save gas by turning off their engine than letting their car needlessly idle, says Consumer Reports' Paul.

Granted it's probably not sensible shutting down the engine every time you get stuck in traffic, but if it looks like you might be at the drive-thru for more than 30 seconds to a minute, it's worth turning off your car, says Paul.

Tips you can use

So what are some fuel-savings tips you can trust?

  • Make sure your tires are properly inflated for starters. Besides posing a safety hazard, underinflated tires can reduce your fuel economy slightly, based on Edmunds.com's 2005 study.
  • Removing excess weight from your car can also help save you gas. The Department of Energy estimates that drivers can save anywhere between 3 and 6 cents a gallon (assuming gas prices of $2.97 a gallon) just by removing those golf clubs and other unnecessary weight from your trunk.
  • If your car comes equipped with cruise control, make sure you use it, especially on long trips. Edmunds.com's study revealed that using cruise control at highway speeds offered an average fuel economy savings of 7 percent.
  • But the biggest fuel saver is driving the speed limit and driving sensibly. Rapid starts and stops and exceeding the speed limit will dent your pocketbook. Just by adhering to one of those, the Department of Energy estimates that drivers can save anywhere between 15 and 98 cents a gallon, again assuming pump prices are at $2.97 a gallon.
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