OP,

A topic close to me at the moment.

Our beater, an 89 Volvo normally gets 360mpg a tank, about 23.5 mpg.

Filled up early, only 10.5 gal + 2oz acetone, but by my figuring it's getting 27.75mpg now. Been running smoother on the 40 mile work roundtrip - which is all that car is used for.

It's hard to believe that I got an 18% improvement, between that and filling the tired 2-3psi over max psi.

A gallon of pure Acetone costs me $15.75 + tax ($17). That's worth about 50 tankfuls, so 34 cents a tank - about 1/160th of it costs to fill my tank, for that improvement, so I'll continue based on what I've seen.

I've heard the argument that maybe it's just cleaning out the engine. Bullshit. It's been having problems idling for the past year. Added octane boost multiple times which seemed to help, fuel injector cleaner, all recently.