An article in a recent Wall Street Journal points to serious problems for boaters as a result of ethanol being used to replace MTBE as an additive in gasoline.
According to the article, condensed water in the boat's fuel tank causes the ethanol to separate from the gasoline. This creates a situation where the bottom of the tank has an ethanol and water mix and the upper part of the tank has a seriously reduced octane fuel. Engines don't like to run on reduced octane fuel, and they really don't like being force fed ethanol and water. Two stroke outboards, twenty years old and older, are particularly sensitive to this and can be permanently damaged. The article further contends that all older hoses and components made with natural rubber (including O-rings) will be damaged and that ethanol is very caustic to fiberglass and possibly also to aluminum fuel tanks.
According to the article, which quotes a spokesman from BOAT/US, Chuck Fort, a purported expert on boat maintenance, ethanol is a powerful solvent. Separated from the gasoline, it will dissolve the residue on the inside of the tank and further contaminate the fuel with particles and debris. It will also, according to Fort, accelerate deterioration in fiberglass and possible aluminum fuel tanks. Fort went on to say that owners of boats with fiberglass tanks will have to replace the tanks.
While following up on this story and reviewing various chemical resistivity charts for ethanol (a.k.a. grain alcohol, hydroxyethane, ethyl alcohol) I could find no evidence to support the assertions that ethanol is caustic to these materials and/or likely to cause rapid deterioration in rubber, fiberglass compounds or aluminum. In fact, according to the chemical resistivity chart published by the Cole-Parmer Instrument Company, ethanol is less caustic than grape juice. It's also lighter than water and evaporates rapidly in air.
Meanwhile, I also found this on the web:
Table 1. Comparison of MTBE and ethanol properties (Rice, 1999).
Ethanol compatibility with metals and nonmetals
Ethanol and ethanol blends of gasoline conduct electricity
whereas unblended gasoline is an electrical insulator. Thus,
pure ethanol is more corrosive than gasoline, and materials-
compatibility is an issue. Pure ethanol and gasoline with high
percentages of ethanol should not be used with aluminum,
zinc, tin, lead-based solder, or brass fittings. Nonmetallic
materials that will degrade in the presence of ethanol include:
• natural rubber
• cork-gasket materials
• leather, polyester-bonded fiberglass laminate
• polyvinyl chloride, polyamides
• methyl-methacrylate plastics
Rice, D.W.; G. Cannon, editor and R. Depue, contributor,
“Background Information on the Use of Ethanol as a Fuel
Oxygenate,” Volume 2, in Health and Environmental
Assessment of the Use of Ethanol as a Fuel Oxygenate,
December 1999, University of California, Lawrence Livermore
National Laboratory, Environmental Restoration Division,
UCRL-AR-135949, Livermore, California; http://www-
So, what does it all mean? Is ethanol bad or not? Seems in high concentrations it is. But . . . ethanol blended gasoline doesn't have more than approximately 10% ethanol. And yet, if it separates from the gasoline due to an interaction with water, it then becomes a pocket of pure ethanol somewhere in the tank.
Boat owners and boat buyers need to be aware of this issue and keep abreast of technical updates. While the Wall Street Journal isn't exactly the horse's mouth when it comes to technical accuracy on boating issues, the story should trigger further scrutiny. What we need is a Coast Guard bulletin we can trust.
Clearly, more information and study is warranted before individual boat owners embark on the costly enterprise of replacing their fuel tanks.
One thing for certain, if indeed water causes ethanol to separate from gasoline, it makes sense for boat owners to refresh their fuel often by making sure they burn what they fuel up with (not keep it stored for extended periods of time) and change their filters frequently. But this is something you should be doing regardless.