He said that acetone expands and constricts rubber.
The mechanic says that's what acetone will do to a fuel system and could damage an engine.
"Putting acetone in your fuel system will deteriorate the gaskets, the fuel pumps which are made out of plastic and the fuel injectors which have rubber o-rings and seals," said Brian Cowie from Ess Auto Fleet.
Another mechanic said acetone does increase gas mileage, but because it runs hotter, he doesn't recommend using it all the time.
"You probably pick up, depending on your vehicle, anywhere from one mile to five miles per gallon," said Randy Newbury from Love Field Auto.
The mechanics say acetone also eats away paint if it's spilled on the car.
Experts dismiss acetone as a fuel additive because they could not recreate the fuel savings in a lab experiment.