USPS Compass

Ethanol & cold-weather engine care

With winter layup upon us, many boaters need to know how to avoid long-term storage problems with fuels containing 10 percent ethanol. This E-10 fuel can attract more water and “phase separate” over time, causing internal engine damage and possible engine failure. BoatU.S. offers these tips to prevent engine damage:

  • Top off your boat’s fuel tanks to about 95 percent full, leaving room for expansion. An almost full tank limits airflow through the vent, which reduces the chance of condensation adding water to the fuel. If you boat over the winter, topping off your boat’s gas tanks between outings will also help prevent condensation.

    (Note: Some mechanics mistakenly advise you to leave a tank partially filled, so you can “freshen” the old fuel by topping off the tank in the spring. However, leaving a tank partially filled with E-10 invites phase separation, which cannot be remedied by adding fresh gasoline. Once E-10 separates, the water remains at the bottom of the tank.)

  • Don’t drain E-10 from your fuel tanks. Although it eliminates any chance of phase separation, this potentially dangerous practice is not recommended.

  • Don’t bother with additives and water separators once phase separation occurs. They won’t help. Having your tanks professionally drained is your only option.

  • Know what your fuel tank is made of. Ethanol can cause fiberglass fuel tanks, many of which were built before the mid-1980s, to deteriorate and fail. Unless your boat’s tank was built to withstand ethanol, you should avoid using E-10 gas (which may not be possible) or replace the tank with a nonreactive material such as aluminum.

  • Never plug up a fuel tank vent to prevent moist air from entering. Without room for the fuel to expand, the tank could build up enough pressure to rupture fuel system components.

  • Add a stabilizer for long-term storage. But understand that stabilizers do not prevent phase separation.

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