Dirty Cars Are More Fuel Efficient

posted: 04/11/12
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As seen in "MythBusters: Dirty vs. Clean Car."

Finding: BUSTED

Explanation: In 2002, an engineer named Tom Wagner Jr., in an article on money-saving tips, reported improved fuel efficiency after giving his car a scrub down. And ever since, auto experts have debated whether the opposite might be true. But the MythBusters scored a point for the enterprising engineer by proving that the only money you'll save motoring around in a dirty car is quarters at the car wash.

People driving the dirty car myth argue that the grimy coating improves aerodynamics, much like the effect of dimples on golf balls. Those tiny divots disrupt air particles as they flow across a golf ball, reducing wind resistance — also known as drag — and sending it sailing 37 percent farther than a smooth ball would travel.

But randomly distributed dirt particles do just the opposite on cars, creating more drag as air particles cling onto the grime. According to MythBuster calculations, that filth effect cuts fuel economy by around 10 percent.

If only that dirt could magically form a golf ball-like dimpled shell on a car's exterior, this myth would be a hole-in-one.

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