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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
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
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
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
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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