Ethanol Gasoline in Marine Engines

LakesOnline.com
Posted: 11/19/2008

Your boat’s greatest enemy may be its fuel. There are a number of reports in the press about the negative effects of ethanol in marine fuel tanks -- this is a concern for boat owners.

The problem began when many areas began banning the use of methyl tertiary-butyl ether (MTBE), replacing it with ethanol blends. This ”new” fuel, referred to as E-10 (10 percent ethanol, 90 percent unleaded gasoline), was not designed with the fuel needs of marine engines in mind. Unlike fuel tanks in autos, boat tanks are vented to the air. Ethanol attracts a significant portion of its weight in water, especially in warm, humid climates. When this occurs, the ethanol and the water separate from the fuel and settle at the bottom of the tank. The result is goo in the fuel systems, clogged filters and stalled engines. If that isn’t bad enough, ethanol has negative effects on fiberglass tanks because the ethanol dissolves fiberglass.

Ethanol will attach to water and that combination will sink to the bottom of the tank, separating from the gasoline. When the engine is started it will be operating on only ethanol and water. In fuel systems where oil and fuel are premixed, no lubrication is supplied to the engine. Without lubrication, engine failure will be immediate. In older two-cycle engines that use premixed fuel, the ethanol has a tendency of cleaning the oil off the cylinder walls resulting in wear and overheating.

Newer outboard motors are calibrated for ethanol gas; however, older outboards could experience problems. Ethanol can reduce the octane numbers by as much as three percent. This can result in pinging or poor performance. Be sure to inspect your fuel filters often. When you are running your boat regularly, be sure to keep the tanks full. This will reduce the amount of air flow in and out of the tank with changes in temperature. At the present time there is no practical additive that can correct the separation issue. The only real solution is to keep the water out of the tank. If you are going to put your boat up for any length of time, completely drain the tank. If that is not possible, fill it as full as possible and do whatever is necessary to keep air out of the tank.

Some of the plastic/butyl/composite hoses, o-rings and gaskets that can be found throughout the propulsion system can be affected by the properties of ethanol. Keep a close eye out for any premature deterioration in these items. In addition, clean and/or change fuel filters regularly. In fact, some boat owners have added a second filter in their systems for protection.

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