• Much of the gasoline sold throughout the United States contains ethanol. The maximum ethanol content allowed by law for use in outdoor power equipment is limited to 10% (E10). Make sure the gasoline you purchase for your outdoor power equipment contains no more than 10% ethanol. If the filling station pump is not labeled with the ethanol content, ask the station attendant what percentage of ethanol is in the gasoline.
• Ethanol can dissolve varnish and gum deposits that have previously formed inside fuel storage cans or the equipment’s engine. When these deposits become dislodged, they can mix with the fuel and plug small openings and filters within the fuel system.
• Ethanol attracts and mixes with moisture in the air, causing corrosion to metal components in the fuel system. If enough water is absorbed, the ethanol and water will settle out of the gasoline blend and settle to the bottom of the equipment’s tank. The layer of gasoline left floating on top has a lower octane level than the original ethanol gasoline blend, which can result in unstable engine operation, power loss and major engine failures.
• Since the fuel is often drawn from the bottom of the fuel tank, the engine is drawing in a mixture of ethanol and water with no gasoline and no lubricating oil. This ethanol/water mix is thicker than gasoline and cannot easily pass through the fuel system. This can result in hard starting, unsafe high idle speeds, stalling, and can ultimately lead to engine damage or fuel system failure.

Guidelines for using E10 gasoline in STIHL power equipment:

If the proper precautions are taken, gasoline containing a 10% quantity of ethanol can safely be used in your STIHL products.

• Use a minimum of 89 octane gasoline and always use fresh fuel. Only buy enough gasoline that you can easily use up within a two-month period or use a specially formulated fuel mixture like STIHL MotoMix