Since airplanes have that big fan (propeller) blowing across the engine, they tend to run cooler and so the % oil tends to be less. Also, most plane fuels use pure synthetic oils. Synthetic oils have a low flash point compared to the oils (mostly castor) used in car fuels. One thing you don't want to have happen is for the oil to burn off and not do it's job. Can you get away with running plane fuel in your car? Sure. But it's not recommended.