There has been trend toward using motor gasoline in aircraft engines. Gasoline engines intended for use in aircraft were designed for and should be run on one of the ASTM specified grades of aviation gasoline. Most major engine manufacturers specifically exclude motor gasoline from the approved fuels list. For a number of reasons, the use of motor gasoline in aircraft is NOT recommended. Motor gasoline is manufactured to much looser specifications than that of aviation gasoline. Quality and performance vary widely from refiner to refiner and from location to location. Quality control and quality ensurance in motor gasoline is much less stringent. The risk of contamination is also greater due to less careful handling. Also, many components of motor gasoline, especially detergents and oxygenated fuels, are quite variable in type and proportion and are generally not known or readily detectable. Motor gasoline has a much wider distillation pattern than avgas. This can result in poor fuel distribution, poor anti-knock component distribution, and excessive motor oil dilution. Motor gasoline is generally more volatile than avgas and could lead to increased vapor-off, vapor lock and carburetor icing. The anti-knock properties of motor gasoline are also different. While the octane ratings appear similar in number, the tests are conducted differently and are not comparable. The stability of motor gasoline is also much lower than avgas. It will form "gum" much more readily leading to deposits on fuel system and engine components. This can result in fuel system malfunction, filter clogging, or engine problems such as valve sticking. The presence of aromatic, or ring, hydrocarbons are not limited as they are in avgas. Because of their solvent characteristics, they may present problems to certain aircraft components. The presence of oxygenated compounds is quite common in motor gasoline, can cause compatibility problems with fuel lines, seals, gaskets and fuel tank materials. Oxygenated compounds also increase the tendency of fuel to hold water. Also, many other additive that are permitted in motor gasoline are not permitted in aviation gasoline. Some compounds used to control knock inmotor gasoline can result in more corrosive combustion products. Motor gasoline today is also generally unleaded or of extremely low lead content. This can lead to excessive valve and valve seat wear. One of the most basic issues is safety. The quality of motor gasoline is not an issue in automobile safety. The quality of fuel in aviation is of critical importance to safety. Highest quality fuel can only be ensured through the use of ASTM specification aviation gasoline. The responsibility for the consequences resulting from the use of motor gasoline in aircraft is directly borne by the owner or operator who chooses to do so. The possible risks to safety and to aircraft engines and components are hardly outweighed by economic or availability issues. The use of motor gasoline in aircraft is neither recommended nor wise.

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