They think?

 

Naphthalene, xylene, and acetone (as well as some others I am missing no doubt) are all used in various engine cleaners/octane boosters -- generally suspended in a mineral oil base.

Will they increase gas mileage? I have no idea. I do remember a class action suit against one of the octane boosters years ago that involved acetone. I *think* it had more to do with fuel line damage than engine damage -- but would need to poke around a bit to confirm. I do remember that some of the guys who ran 100LL in their 80L planes found the higher octane gas which contained acetone would sometimes eat their carb floats ...

 

I'm just guessingthat's what they're dong. I'm not entirely sure a cognitive specialist would recognize it as such, but I'm not an expert