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Ethanol Fuel - What you should know


Phase Separation

What are ethanol and ethanol-blended fuels?

Ethanol is used as an “oxygenate” and is added to fuel to help reduce hydrocarbon emissions that cause air pollution. It is highly refined grain alcohol, approximately 200-proof, produced from natural products.

In the U.S., ethanol is typically produced by removing the starch or sugar portion of corn and fermenting it. The fermented starch is then distilled into alcohol. Excess water is removed, resulting in very pure, 200-proof, ethyl alcohol (ethanol).

The term “ethanol-blended fuel,” or E10, refers to fuel that contains 10% ethanol and 90% gasoline. Similarly, E85 refers to fuel that contains 85 percent ethanol and 15 percent gasoline and is intended only for engines specially designed to accept high-ethanol content fuel blends. Not all states require gas pumps to be labeled to indicate the presence of ethanol in the fuel, so you may be currently using E10 fuel and not be aware of it.


Problems with the transition to E10 fuel;

The most likely time for fuel problems to occur is when you first begin using ethanol-blended fuel. When E10 is added to a fuel system that has been using non-ethanol gasoline, ethanol, as a new solvent, will tend to dissolve and loosen deposits that are present in the tank and fuel system. Phase separation may occur, resulting in an approximately 50/50 ethanol and water layer at the bottom of the fuel tank. To limit problems with a changeover to E10:

  • Check for the presence of water in the fuel tank. Inspect the water-separating fuel filter on larger engines. If water is found, pump the tank dry from the fuel line or siphon the tank dry. Examine the fuel in a clear container. If the fuel is not clear or has a sour odor, the tank should be cleaned.

  • Add a quality cleaner to help clean deposits in engine

  • Completely fill the tank with E10 fuel to maximize the amount of ethanol in the tank to absorb any water present.

  • Monitor filters and carry extra fuel filters to deal with filter-clogging concerns.

Phase separation with E10 fuel;

When E10 gasoline comes into contact with water, ethanol will allow fuel to absorb water. This is actually somewhat beneficial, but fuel can reach a saturation point and water can phase separate to form a distinct layer in the bottom of the tank. The upper layer is gasoline, depleted of ethanol and now has a reduced octane level. The lower layer is a corrosive mix of water and ethanol. No chemical agent or fuel additive can be added to E10 gasoline, in a reasonable quantity, that will fully prevent phase separation or recombine a phase-separated layer.


Use E10 only, not E15, for your boat!

We still don’t know how and when E15 will be offered for sale, or if it will ever be sold in your local marina. We do know, however that you don’t want it in your marine engine. Experts are unanimous on the subject. According to Mercury Marine: “Fuel containing higher proportions of ethanol is not compatible with many fuel system and engine components and, if mistakenly used, will cause irreversible damage to these components that will lead to engine failure and potential safety risks.” At this time, we can only warn you about the possibility of confusion and the risk of accidentally filling your boat’s gas tank with E15.


To keep your engine and fuel system safe;

  • Do not put any fuel containing more than 10% ethanol (E10) in your boat’s fuel tank or outboard motor (EPA’s decision only applies to 2007 and newer highway vehicles), unless your owner’s manual specifically states otherwise.

  • Check the pump to be sure that it is dispensing E10. Some gas pumps at local gas stations may offer both E10 and E15, or have blender pumps that dispense mid-level ethanol fuels for Flex-Fuel automobiles. Higher ethanol fuel (E15) may be less expensive than regular (E10) fuel, but putting E15 into an E10 approved vessel could cause engine and fuel system damage.


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