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More Miles Per Gallon, Please

Gizmos that may take you for a ride

In these days of high gasoline prices and long vacation road trips, get ready for high-gear hawking of gadgets that promise more miles per gallon.

See also: Cut car and gas costs.

Some of these gizmos improve mileage by 20 percent or more, promoters claim, by harnessing special science. "Approved by the Federal Government," you're told. Breathless customer testimonials for the devices, available online and at select bricks-and-mortar retailers, further bolster the allure.

Gasoline saving devices don't actually save money

Harry Campbell

Gas-saving gizmos that promise more miles per gallon may be a waste of money.

The products typically cost $50 to $250. But buy them and you'll just be taken for a ride, experts say.

"I've been testing these devices for a very long time, and to date haven't found a single one that lives up to its claims," says Mike Allen, senior automotive editor at Popular Mechanics magazine. "In the last round, I tested eight different types. Five did nothing, two actually increased fuel consumption and one set a car on fire."

After its own tests on various gadgets, Consumer Reports issued a "don't waste your money" warning, echoed by the Federal Trade Commission and the Better Business Bureau. The Environmental Protection Agency has tested (but never endorsed) more than 100 such devices and found that none significantly improve mileage and some may damage your engine.

If you closely follow the owner's manuals that come with some of the devices, you may get a marginal boost in mpg. But this may not be because of the device itself. "The advice is usually to install the device and properly maintain your car, avoid jackrabbit starts and do other common-sense tips found at," says an EPA spokesperson. "Guess what? Do those things without the gadget and you'll save fuel."

The Scientific Explanation

  • Promoters claim fuel-line magnets will break up "clumped" fuel molecules so that gas burns more efficiently. "But gasoline molecules don't clump up," Allen says, "and … don't respond to magnetic force."

  • Engine ionizers clip to spark plugs, supposedly to increase combustion efficiency. But in tests, Allen says, increased combustion served to decrease power — and triggered an engine fire.

  • Vortex generators are said to mix fuel more efficiently with air. What they really do is reduce the air flowing into the manifold, reducing power.

  • Vapor injectors are said to convert raw fuel to vapor outside the engine for better performance. In reality, engine computers prevent any such benefit.

  • Water injectors use technology that provided emergency power in World War II planes. But tests show this technology doesn't work in automobiles.

  • A device that plugs into a cigarette lighter is claimed to "smooth out noise" in electrical systems and increase mileage. No such gain was found in tests by Popular Mechanics and Consumer Reports.

So what does the device do? "It lights up when you plug it in," says CR's Sue LaColla.

Sid Kirchheimer is the author of Scam-Proof Your Life, published by AARP Books/Sterling.