Ethanol Problems and Outboard Engines

Ethanol problems can cause all kinds of performance issues. Problems like stalling, contaminating the fuel system by releasing gunk and sludge throughout the engine, clogging of fuel filters and carburetor jets, eroding of engine parts like fuel lines carburetor gaskets and possible engine failure.

Ethanol fuel economy is about 3% less than straight gasoline. Adding ethanol to fuel was designed to reduce the amount of fuel emissions released into the atmosphere and replace MTBE. Sounds like good enough intentions but that’s where the positive ends. In fact that is the only positive result I could find in the program. Now, new proposals call for ethanol expansion to increase the amount of ethanol to 15%. The experts agree, that ethanol above 10% will cause damage and performance problems with outboard engines.

In researching the pros and cons of ethanol fuels, in some states, you are forced to purchase E10 at the pumps. There is no good news when it comes to outboard motors.



  • Reduces fuel emissions
  • replaces MTBE (a cancer risk)
  • Ethanol has a strong attraction to moisture increasing the amount of water accumulating in your fuel tank
  • E10 fuel’s usable life span may be less than the normal length of off season boat storage
  • Phase seperation
  • Reduced fuel economy
  • Ethanol produces less energy (BTU’s) than an equivalent unit of gasoline
  • Ethanol cleans gum,varnish and surface corrosion in your boat's fuel system
  • Ethanol cleans gum,varnish and surface corrosion in the transport tanks in the fuel distribution system
  • Ethanol may dissolve plastic resins used to make some fiberglass boat tanks

What you can do to minimize the possibilities of damage to your engine due to ethanol problems.

  • If it's possible in your area, avoid E-10. In most states it is required by law to post a warning that the fuel in that pump has E10 Ethanol added.
  • Use fuel stabilizer in every fresh tank of fuel. Stabilizers do not help fuel that has already aged.
  • Always keep your tank topped off to eliminate the empty space where moisture can accumulate, causing phase seperation.
  • Use a water-separating fuel filter.
  • Carry a spare filter on board.
  • Drain the carburetor floats if you are going to leave the boat set up for a long period of time; exp. winter storage.
  • Buy name brand fuel.
  • Buy fuel from the same source if possible.
  • Buy fuel from stations that have newer, cleaner storage tanks.
  • Use a higher octane of 90 or above.
  • Check the manufacturers cautions on how to prevent damage that can come from the use of E10 fuel.

Some other suggestions, when switching over to ethanol fuel, include draining your fuel tank, having your tank mechanically cleaned or even replacing it.

Recent fuel testing revealed that the % of alcohol (ethanol) present at the pump, varies widely. Below 10% ethanol is considered acceptable by most marine engine manufacturers. There are Fuel Test Kits you can purchase to measure the amount of ethanol in your tank. E10 is not stable and can change after pumping into your boat tank. You can also use these kits to check the level of ethanol fuel at the pump. Not all states require labeling of pumps that have E10 added to their fuel.

For more information on ethanol problems caused by ethanol-blended fuels and outboard motors, check the "FAQ" section on the Yamaha website or the Service and Warranty section of the Mercury Marine website. Evinrude also has information on outboard engine damage and ethanol fuel.

Every state differs on their regulation and laws pertaining to ethanol and fuel.

Find out what your state law requires regarding labeling at the pumps to let the consumers know whether E-10 is included in their fuel.

The FAA bans the use of alcohol-blended fuels in aircraft citing the dangerous effects it has on engines. If the government bans it from aircraft, why are they forcing us to use it in our vehicles and boats? It's hard not to debate the politics behind their decision making but it sounds like a hasty policy to satisfy another lobbying group. Truth is, the government looked at the marine industry as only 5% of the total fuel consumed in the U.S. and the governments response is they're really not concerned with what effect ethanol problems might have on such a small minority.

Marine-Related Ethanol Lawsuit Passes Motion to Dismiss in Florida

"Boat Owners Continue to Struggle with and the Effects of E10 Fuel-The issue of ethanol in the fuel tanks of marine engines continues to cause problems for boaters nationwide. A Florida lawsuit, alleging negligence against six oil companies for failing to warn boat owners of potential ethanol problems caused by E-10 blended gasoline, survived a motion to dismiss from the defendants. This is a significant milestone for many boat owners who have been forced to repair and replace marine engine systems due to a lack of knowledge of the destructive effects of E10 fuel.

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