Engine-cleaning additives in gasoline aren’t just a marketing gimmick, AAA said in a new research report.

The travel group found “significant differences in quality” between Top Tier gasoline, which is billed as healthier for car engines, and fuel sold at other U.S. retailers.
Gasoline acquired from retailers that don’t sell Top Tier fuel caused 19-times more engine deposits after 4,000 miles of simulated driving, based on the test results.

AAA noted that carbon deposits can reduce fuel economy and hurt vehicle performance, as well as increase emissions.

Top Tier, a program backed by automakers, sets standards for gasoline and higher-quality additives that keep engines clean.
Only one-third of all U.S. gas stations meet the criteria. Exxon, Mobil, Chevron (CVX), Valero and Costco (COST) are among the retailers licensed to sell Top Tier gasoline, according to Top Tier’s website.

AAA also conducted a survey of American motorists, saying most consumers believe there is a difference in quality from one gas station to another. But just 12% of drivers buy gasoline based on the package of detergent additives. Rather, consumers said they primarily consider location and price when choosing a gas station.

Top Tier-labeled gasoline costs an average of 3 cents per gallon more than other gasoline brands over a 12-month period, AAA said.

Greg Brannon, AAA’s director of automotive engineering, said drivers can reverse the buildup of some engine deposits by switching gasoline brands.

“After a few thousand miles with Top Tier gasoline, performance issues like rough idling or hesitation during acceleration can often be resolved,” he added.

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