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The Effects Of Ethanol Blended Fuel On Boat Engines

As blends of gasoline are sweeping across the nation and Tennessee, boat owners may have questions about the affect of these fuels and their boat engines. There are two types of ethanol blended fuels that are currently available at retail fueling facilities in Tennessee:

1. E10 – A blend of 90 percent gasoline and 10 percent ethanol, by volume

2. E85 – A blend of 70-85 percent ethanol and 30-15 percent gasoline, by volume. E85 fuel ethanol is a fuel intended for flex-fuel vehicles only. It should never be put into any engine that is not specifically designed for E85 fuel.

There are a few situations that boaters need to be aware of while making the transition to gasoline-ethanol blended fuel.

First of all, ethanol is a solvent. If there is any gunk or residue in fuel tanks, then the ethanol may dissolve these, clogging filters. The good news is that after 2-3 tanks of gas, this should not be a problem anymore. Boaters need to carry and be ready to change fuel filters (10-micron filters work well), more often until a few tanks of gasoline have been used.

Not all fuel hoses are compatible with ethanol, especially pre-1990 fuel systems. Boaters need to check hoses and make sure they are marked J-1527.

Most fiberglass fuel tanks do not resist ethanol. Ethanol can break down the resin and create a sludge that bypasses the filter and wrecks the engine. Unless a boat’s manufacturer can confirm that a fiberglass gas tank was built to withstand ethanol, it is recommended that the tank be replaced with another material such as aluminum, stainless steel, or polyethylene tanks.

Ethanol attracts moisture and as a result, when a boat is idle for a long time and the fuel tank only partially filled, then water and gas could separate, leaving the water/ethanol blend in the fuel tank at the bottom of the tank. When this happens, filling the tank with fresh fuel will not fix this situation. Fuel stabilizers help the gas stay fresher longer, but it will not prevent this phase separation. The best recommendation is that if the boat is going to be sitting for a while, then keep the boat’s fuel tanks filled to about 95 percent capacity.

Most marine manufacturers warranty engine and parts for E10 ethanol but not for higher concentrations of ethanol.

What not to do:

Do not drain fuel tanks of E10 gas. While it does eliminate any chance of phase separation, it’s not practical and potentially dangerous and not recommended.
Do not try to plug up a fuel tank vent to prevent moist air from entering a tank. Without room to expand, the additional pressure could rupture fuel system components.
Do not install a water separator thinking it will prevent phase separation. Ethanol readily absorbs water which will burn safely through the engine. But if ethanol-enhanced gasoline does become saturated, an engine will not run on the water-soaked ethanol solution, which sinks to the bottom of the tank.
Do not use E85 in any boat.
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