Many motorists are clogging their car’s engine by not using gasoline with enough added detergents.

That’s the conclusion of a study released Thursday by the AAA auto club.

Federal rules in place since 1996 require all gasoline to have some engine-cleaning additives, but many major brands have extra detergents. AAA says its tests found that lesser gasolines left 19 times more engine deposits than so-called top-tier fuels after the equivalent of 4,000 miles of driving.

AAA says gasolines with extra detergents cost an average of 3 cents per gallon more. And that could be their undoing.

Three-fourths of consumers surveyed by AAA buy their gas based on price or the service station’s location. Only 1 in 8 picks a brand because it has extra detergents.