The Effect of Mothballs in a Gas Tank

by Clare Edwards

A long-running urban legend holds that putting a few mothballs in the gas tank of your car every time you fill it up will improve the mileage and performance.

The Story

The "mothballs in your gas tank" legend has been going so long that it has several variants. Sometimes mothballs alone are recommended, sometimes mothballs and another additive, such as alcohol. A recent version starred a pill made from mothball ingredients, according to the Science Show website.

Expert Insight

Chemists and car experts alike roundly dismiss the mothball story. At best, according to NPR's Car Talk radio show, some mothballs (the kind made from naphthalene) could raise the octane of your fuel slightly but with no significant effect on performance.


Not only do naphthalene mothballs do nothing for performance, claim scientists at the U.S. Department of Energy, but too many of them could cause a buildup of carbon deposits in your engine. Other varieties could produce hydrochloric acid, which could permanently damage your car.

More Articles

article divider