"...I'm just not buying this..."
Does the acetone improve mileage on new engines as well as on older engines? I am thinking that the acetone might be cleaning the fuel injection system and making it more efficent. 0.25% acetone in gasoline (10ml/gal = .33 oz/128 oz 0.25% acetone) is, I would think, insignificant in terms of energy effects, unless there is some synergism going on that we don't understand.
I am also running a 2003 KIA, with 45,ooo miles on it. It gets 32 mpg w/out acetone and 35+ mpg with acetone. Not a big change, but a measurable change. My working theory is that the small effecient engines don't see the big benefit of increased milage as much as larger engines.
also.....I don't think the increase is due to cleaned injectors, because the Explorer that I am running never did get 20+ mpg....even when new.....but I regularly get 20+ mpg using 9 mL acetone / gal. gas.