Why Should You Winterize Boat Fuel?

Before ethanol, we didn’t have to worry much about storing boat fuel for the winter. Add a stabilizer and the gasoline would be fine in the spring whether you had a full or nearly empty tank. Ethanol-infused fuel has changed the rules particularly in our colder Alaskan winters.

Today’s E10 fuel is a gasoline/ethanol blend. The ethanol in the gasoline absorbs water and distributes it throughout the gasoline. As the ethanol soaks up and distributes more and more water, it may result in engine sputtering, jolting, power loss, poor fuel economy, and corrosion.

Water gets into fuel tanks through:

  • leaky gaskets on the filler cap, hose cracks
  • condensation inside the tank when temperatures change
  • previously contaminated fuel
  • ethanol’s innate ability to attract water from the surrounding air, which accumulates over time

When there is water contamination in small doses, it is usually burned in the combustion cycle without harm – when the fuel is being used on a regular basis. Storing fuel for long periods means water from leaks, condensation or absorption won’t get burned off and the ethanol can keep taking on water. If conditions are right, the accumulation of contaminants, when storing fuel over a typical Alaskan winter, can often exceed the ethanol’s absorption ability and phase separation can occur. Phase separation is when the gasoline and water rich ethanol separate into distinctive layers, with the corrosive ethanol-water mixture sinking to the bottom of the tank. Phase separation is also more likely to occur in winter, especially if the fuel is not being used. Temperatures that fluctuate from warm to cold or freeze/thaw also increases the amount of condensation, reducing fuel stability.

When ethanol has separated from gasoline, there is no additive that will fix the problem or reverse the phase separation. Running motors after a long period of sitting can damage seals, O-rings, injectors, and other delicate engine parts.


  • When storing boat fuel for the winter fill the tank completely. Partially full fuel tanks leave more surface room for condensation. With a full tank, there is no room for condensation.
  • Add stabilizing treatments in the fall before storing the fuel. Allow the additive to circulate through the fuel system before you store fuel for the winter.
  • Alternatively, completely empty and clean the fuel out of the tank and check for any condensation prior to filling the tank again at next use.
  • Check hoses, caps and clamps for signs of cracks or deterioration and replace any damaged components.


  • With small amounts of water, pumping it out of the tank or treat the fuel with a drying agent are options.
  • If a higher quantity of water and/or sludge are detected, the fuel and the tanks may need to be cleaned. In extreme cases the fuel may need to be discarded, the tanks cleaned and then refilled with fresh fuel.
  • If the tanks are old and corroded and with blocked filters the fuel will need to be removed, and the tanks inspected and potentially replaced.

Do customers complain about water contaminated fuel being dispensed from your bulk fuel tanks? Frontier Fuel Service can test for and remove water contamination of bulk fuel to ensure that your customers are receiving a clean product. Contact Frontier Fuel Service if you would like to know more.

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