Ready for me to throw a wrench in this theory?
Mythbusters also tested whether or not air conditioning affected MPG. Well, it did not and in fact the vehicle using AC was able to continue the course for a while after the car without the AC ran out of gas.
They also said that was inconclusive being that the shows safety crew would not allow them to drive higher than 45mph which reduced the drag that would normally be caused by the windows being rolled down.
45 and under AC MPG may be less effected but anything above 50 you would have to think the aerodynamic drag having the windows down would cause more fuel usage.
Oxford White 2015 Premium GT with 50-Year Pkg | 3.55 Gears | Roush CAI (105mm Velocity tube) | Stainless Works Headers (Jet-Hot ceramic coated), high flow cats, H-Pipe CatBack full 3" with 4" tips| BAMA V2 93 Octane Tune | Baer EradiSpeed-Plus 2-Piece Rotors | JLT 3.0 Oil Separators | FRPP M-20201-M STB | Silver PP Wheels 19x9, 19x9.5 | NITTO G2 255-40-19, 275-40-19 Tires | J&M Jacking Rails & Subframe Alignment Kit | Steeda Subframe Connectors & Bushing Supports | BMR Front Subframe Brace | Cervinis 1232 Functional Ram Air hood | Ford Performance door sills | White Madness Garage Chrome Shifter | Diode Dynamics interior LED conversion stage 1 & XP80 reverse light | 3M Dark Ceramic Tint (25% sides/20% rear) | Lloyds "50 Years" floor and trunk mats...
Performance White 2012 Premium Pony Package | Torsen T2R 4:1 TBR | FRPP 3.73 Gears | GT500 Differential Cover | DSS 3.8" Carbon Fiber DS | Airaid CAI | BAMA 93R tune | Baer DecelaRotors (drilled/slotted) | BMR Adjustable Panhard & Brace | JLT Oil Separator | Boss 302 STB | Nexen N3000 255-45-ZR18Y tires | PP Engine Cover | 25% Tint All cars should be rated for Smiles Per Gallon!