What You Need to Know About E-10 Gas
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The octane issue:
Some boaters choose to leave their boat's gas tank mostly empty over the
winter, and then refill in the spring in the hopes of "refreshing" the fuel to
regain any octane loss. However, a nearly empty gas tank introduces a bigger
problem: the strong possibility of phase separation with the E-10 gas.
Incidentally, over long winter storage periods, E-10 gasoline loses octane at
about the same rate as non-ethanol gasoline.
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The path to phase
separation: Ethanol (an alcohol) can attract and absorb water - about 10
times more than regular gasoline - and still burn harmlessly through the engine.
However, there comes a tipping point when the ethanol can no longer absorb the
water, and the alcohol will separate out or "phase separate" from the gasoline.
When this happens, the solution of water soaked ethanol will settle to the
bottom of the tank, which is where the engine's fuel system pick-up is located.
Can you see where we are headed with this?
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More water, less
absorption: The problem with leaving a tank mostly empty is that it
increases the tank's "lung capacity" to breath in moist air (water) through the
tank's vent. If the tank is mostly empty over the winter, there will also be
less E-10 gas in the tank to absorb the moisture. This combination of more water
and less capacity for absorption greatly increases the chances of phase
separation. Adding fresh gasoline in the spring would not remedy the problem -
the phase-separated ethanol remains separated at the bottom of the tank.
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The Water Separator
issue: E-10 can hold up to 1/2 percent of water by volume and up to that
concentration the water molecules will dissolve in the gasoline forming a
soluble mixture that will pass through a water separator and burn harmlessly in
your engine. The only time water will collect in a tank and not be absorbed is
if phase separation has occurred, and by then it will be too late. A water
separator is not a solution to the phase separation problem.
- The Fuel Additive issue: Fuel additives are good for many reasons and should be used when laying up a boat for winter, but no additive will stand up to a good-sized slug of water. And once too much water has entered the tank and the gas has begun to phase separate, no additive will return the fuel to its original state. The only solution to phase-separated gas is to have a professional drain the tank and start anew.
Keep the tank nearly full. This greatly reduces the volume of moist air that can enter the tank via the fuel tank vent when temperatures fluctuate in the fall and spring. With any fuel, an antioxidant (found in many additives) will help keep it fresh during lay-up. Finally, never plug up a fuel tank vent - it creates pressure that could cause dangerous leaks in the fuel system.
For more information go to www.boatus.com/seaworthy/ethanol.asp. A free, downloadable winterizing checklist is available at http://www.BoatUS.com/seaworthy/winter.