E10, Is a gasoline blended with up to 10 % ethanol alcohol and is now in widespread use in the U.S. Ethanol, ethyl alcohol, is made from corn, sugar and other grains. Alcohol is an excellent cleaner, solvent, anti-freeze and most important, ethanol is hygroscopic, meaning it will absorb large amounts of water. Government regulations and laws for ethanol fuel use and labeling differ from state-to-state, and are constantly changing. View Ethanol Handbook 2006 State-By-State Laws. The most serious boat engine problems, resulting from ethanol E10 use, have mainly occurred due to illegal amounts of ethanol (over 10 %) being incorrectly added at the gas station pumps, by the delivery truck drivers.. Since using over 10 % alcohol gas is dangerous, it will invalidate all marine company engine warranties. Many ethanol problems, reported by boaters appears to be due to their lack of knowledge/information on how to properly manage alcohol fuels. Many boat engine breakdowns in recent months are directly related to the mismanagement of E10 gas. Your marine mechanic may not even suspect or test the fuel as a possible cause of breakdowns. Many marine engine repair businesses have flourished as a result of ethanol gas engine damage. Several older engines can not use any fuels that contains alcohol. Eg. Certain fiberglass tanks, mostly manufactured prior to 1992, will decompose from alcohol. Fortunately newer outboard engines (past 5 years) have been designed to be more compatible with alcohol fuels. Reasons Boat Engines Have More Problems with Ethanol Gas: Boaters, often store gas in tanks longer than recommended for E10 (90 days). Cars, unlike boats, usually replace fuel every week or two, which will successfully prevent the possibility of water-contamination/phase separation. Boat engines live in a water environment - Alcohol gas loves to absorb water. Ethanol E10 gas can absorb large amounts of water into the fuel tank, MTBE in conventional gasoline did not. Plus, boat engines usually last longer than cars. Still owning and using a marine engine from the 1970's or 1980's is not uncommon. * These older engine parts and tanks were not usually designed or tested to withstand the damaging effects of alcohol gas. * Several older marine engines (made prior to 1992) have plastic and rubber parts, and fiberglass tanks that are NOT compatible with E10 alcohol fuel.