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Ethanol Fuels and Gas Tank Problems

Fuel Systems > Ethanol Fuels and Gas Tank Problems


Many states are now using ethanol blended fuels and others are considering mandating its use. As a boater there are issues you should be aware of when using this fuel in your boat.

A quick search on the internet reveals numerous articles about problems with ethanol when used in marine environments. The major problems are addressed below.

  •  Ethanol can break down resins and fillers in fiberglass gas tanks, causing them to leak.
  •  Resins leached from fiberglass tanks can go through the fuel system, sticking to valves and other internal engine parts. These deposits have caused bent pushrods and have clogged intake valves.
  •  The alcohol attracts water, leading to increased corrosion in metal gas tanks.
  •  Water in the fuel affects the octane and leads to knocking and decreased performance.
  •  Ethanol acts as an efficient solvent, gradually cleaning out the accumulated gunk in fuel tanks and lines, and clogging carburetors.
  •  Certain rubber gaskets and fuel lines are weakened by ethanol.

Fuel Properties

It helps to know the terminology of fuels being sold. Ethanol is grain alcohol, produced mostly from corn in the U.S. It is used as an "oxygenate," an additive blended with gasoline to reduce exhaust emissions by introducing additional oxygen molecules to the combustion process. Two ethanol blends are currently available in many parts of the United States and Canada:
  •  E10 Ė A blend of 10% ethanol and 90% unleaded gasoline. This is the most common ethanol fuel available.
  •  E85 Ė A blend of 85% ethanol and 15% unleaded gasoline.

Some boat users, particularly those with newer boats or engines, have experienced no ill effects from using E-10 fuels. E-85, however, is classified as an "alternative fuel" and can be used only in "flex-fuel (FFV)" engines. Only those designed to burn high concentrations such as E85 can utilize the unique combustion characteristics and tolerate the corrosiveness of the alcohol. Never put E-85 in your outboard. While the effects of E10 fuel can be mitigated in boat engines, the marine industry advises that using greater than 10% ethanol in your fuel will damage your engine.

Alcohol fuels are very prone to phase separation, when the weight of the ethanol and water will sink to the bottom of the fuel tank and get picked up by the motorís fuel system. (Even small amounts of water can harm the fuel system). Increased water in the fuel also decreases octane rating, so performance and fuel economy are affected. Other problems such as increased stalling, misfire, hesitation and difficulty maintaining boat speed during trolling have also been reported.

Since the 1970s, most non ethanol gasoline sold has a component called MTBE (methyl tertiary butyl ether) added to the base gasoline to increase oxygen in the fuel, boosting octane. Though this additive is being phased out due to concerns over pollution of drinking water aquifers, it still is in use in many areas. Mixing ethanol with MTBE fuels creates a gel-like substance that gums up fuel and combustion systems.

So What Can You Do?

So, what steps can you take to address the problem? If you have an older boat the problems can be even worse. The ethanol may merely accelerate the stress from normal wear and tear of years of use.

  •  First, inspect your fuel tank.
    •  Look for signs of corrosion in metal tanks.
    •  If you have on older boat with a fiberglass fuel tank, you should replace the tank with a new plastic tank. Polyethylene fuel tanks are not affected by ethanol, age well and are incredibly durable. Any boat with a fiberglass gas tank that was not specifically designed for ethanol, especially ones built before the mid 1980ís, are particularly suspect.

    •  Avoid replacing your tank with an aluminum tank. Contact with water and other metals, inside or outside of the tank, causes pitting and crevice corrosion in the marine environment. Contact with water in the bilge, particularly salt water, is especially corrosive over time. Welds on aluminum tanks are another area of weakness. Again, polyethylene tanks are very durable and not as affected by the constant movement and expansion of fuel, which causes stress on aluminum tanks.
    •  Fuel tanks that are above deck are relatively easy to replace. As you would expect below deck fuel tanks are a little harder to get switched out.
  •  Inspect fuel lines and gaskets. Ethanol can affect many plastics and rubber. The alcohol present in automobile gasoline is often not compatible with the rubber seals and materials found in marine applications. Most fuel hoses made after 1984 and marked with SAE J1527 are designed to withstand ethanol. Check for wear, cracks and brittleness.

  •  Pick up a supply of fuel filters to absorb deposits that are loosened from the fuel system. After a few months of use the filters may not have to be changed as often. Consider installing a water separating filter kit if you do not already have one.


  •  Adjust your engine. Your boat engine might run rough or the mixture ratio might be off. You (or your mechanic) might need to tinker with the idle adjustment screws, and low and high-speed air/fuel adjustments.
  •  Never mix older fuels with ethanol. The different properties of the fuels and how they react to water may cause further problems. Evidence suggests that the combination creates a gel-like substance that can clog passages in carburetors, especially in outboards. Run the tank dry before you change fuels. Outboard manufacturers also recommend adding an injector cleaner to the fuel.
  •  Donít let your fuel sit around for a long time. The shelf life of ethanol might be as short as six weeks. Use a fuel stabilizer if you are not using your boat for more than a few weeks. This inhibits oxidation of the fuel, which leads to the formation of deposits. Once fuel has phase separated, fuel additives will not have the desired affect. The water has to be removed and the depleted fuel safely disposed of. Many suggest storing your boat with a full tank. If you needed an excuse to get out and use your boat more, this may be it. With a full tank you are ready to go.
  •  Never run E85 in outboard engines. Fuels containing up to 10% ethanol (E10) are considered acceptable in many engines currently being manufactured. However, fuels containing higher levels of ethanol are not considered acceptable to use and may void manufacturer warranties.

Please consider purchasing any needed fuel system components from us here at iboats.com.

To look at our selection of tanks, filters and components, simply CLICK HERE.

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