What it does?
Ethanol is an alcohol additive blended with fuel to allow for cleaner exhaust emissions. Most fuels in the United States now contain ethanol in amounts from 10% (E10) to 85% (E85). Most fuels are E10, as E85 fuels require engine fuel system modifications to burn. Ethanol is a solvent that in the marine fuel system will dissolve old varnish that has built up for possibly years in the fuel system. This varnish when dissolved will clog fuel systems and cause possible engine damage. Ethanol attracts moisture. Marine fuel systems are vented to the open air to keep a vacuum from forming in the fuel system. Ethanol will draw moisture from the air and mix it with the fuel in the tank possibly causing engine damage.
Adding ethanol to fuel can change the fuels volatility and possibly cause “vapor lock” in the fuel system. Ethanol blended fuels evaporate quicker than non-blended fuels. When the fuel evaporates it leaves behind gum and varnish that can clog a fuel system. When enough moisture is pulled into ethanol blended fuels, they will separate (phase separation) allowing the water to go to the bottom of the fuel tank (where the fuel pick-up is located) and the lighter fuel to float on top. The water is then pulled into the fuel system causing engine damage and fuel system corrosion. In older boats with resin fuel tanks, ethanol will actually begin to dissolve the fuel tank itself.
What can you do?
Use a 10-micron water separating fuel filter to remove varnish, debris and moisture from the fuel system. If your boat or motor is not equipped with 10-micron water separating fuel filter, add an easily installed kit specific to your boating application. Upgrade existing water separating fuel filters to 10-micron filters. Inspect fuel filters regularly and replace at least twice a year.
Marine engines are not currently equipped to operate on E85 fuels. Never fill your fuel tank with E85 fuel. Add fuel stabilizer to your tank EVERY time you get fuel to slow down the evaporation process and keep the fuel “fresh”. When the boat is stored for extended periods of time without use (4 weeks or longer), keep the fuel tank almost full. The less air in the fuel tank the less moisture the ethanol can draw from air. Allow for expansion, especially if you keep your boat in rack storage. Fuel from a completely “full” tank can expand with temperature changes and force fuel out the vent and onto the boats below yours in the storage facility.
Allow inboard and stern drive engines to idle with the blower running and if possible the engine hatch raised after running the boat in hot weather or under high load applications (skiing, tubing etc.) for five to ten minutes. This will keep your engine from “heat sinking” (your engine gets hotter after you shut it off because there is no water cooling the engine and unlike a car, the engine is located in a small tight compartment where heat builds up) and vaporizing the ethanol fuel causing vapor lock. The vaporized fuel will not allow the engine to start and will usually lasts just long enough to ruin your afternoon and get you towed back to the dock, when by that time the engine has cooled down and starts without problem. Do not mix ethanol-blended fuels with fuel that has MTBE as a way to raise the octane level. When mixed the fuels will react causing a gel like substance to form and clog the fuel system. Most fuel outlets in the United States have stopped adding MTBE to their supply since late 2006, but it can still be found in some areas.