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Is Ethanol Damaging Your Boat Motor?

October 12, 2015

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With the increasing prevalence of ethanol blended gasoline over the last several years, there has been a lot of talk concerning the potential damage that ethanol can inflict upon outboard motors. Corrosion, rotted fuel lines, water contamination, and a whole host of other problems have been blamed on the small percentage of ethanol contained in most modern gasoline. So will ethanol be the death of your boat motor? The answer, according to the manufacturers of outboard motors, is probably not.

Many of the problems associated with ethanol blended gasoline are either misattributed or easily prevented. Ethanol’s supposed tendency to absorb water out of the air is just not true, according to a Mercury Marine’s “The Myths of Ethanol and Fuel Care”, “The primary cause of water collecting in fuel tanks is condensation from humid air.” This condensation can occur whether the tank contains E-10 or regular gasoline. Ethanol can absorb a small amount of water after it has condensed, but this can pass safely pass through the engine. The best way to prevent excess water from entering a fuel tank is to keep it full of fuel, reducing the amount of room for air.

Ethanol is an effective solvent, which can cause issues if using E-10 for the first time in a tank that has been previously used with regular gasoline. The new fuel can dissolve leftover residues, causing a gummy substance to form in the tank. This should only be an issue when first making the transition to E-10, and can be remedied by thoroughly cleaning the fuel tank or, as Honda and Yamaha suggest, installing a 10 micron fuel filter between the fuel tank and the motor.

Honda, Mercury, and Yamaha, Three of the largest manufacturers of outboard motors, specifically state that their products are warranteed for use with E-10 ethanol blended gasoline. They do recommend a few precautions, such installing a fuel filter and using a fuel stabilizer if the tank will sit unused for a long time. One important detail in all three of the manufacturer's recommendations is NOT to use any fuel containing more than 10% ethanol, such as E-15 or E85, as these fuels can void the warranty and damage the motor.

  More information on ethanol blended fuel and the myths surrounding it, check out these articles from BoatUS and West Marine.



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