This post was written by ghoj on October 31, 2012
Posted Under: Boating Topics

There has been a lot of discussion in recent years about the effects of E-10 fuel on marine fuel systems since it was introduced in 2006. E–10 is a mixture of 10% ethanol with 90% unleaded 87-octane gasoline. The purpose of adding the ethanol is to extend the fuel and reduce emissions. However, since the ethanol is less potent than gasoline, fuel economy actually decreases by 5-8 % in automobiles and presumably has the same effect on marine engines.

Since ethanol has the properties of a solvent, it had a negative effect on the marine fuel systems of the day. Some of the problems are as follows:

1) The fuel lines, fuel fill hoses, vent hoses and primer balls tend to swell and degrade with E-10 fuel.

2) Fiberglass tanks will start to degrade. The ethanol slowly dissolves the resin in the fiberglass weakening the tank and contaminating the fuel. This has caused major repairs in boats like Bertram.

3) Any corrosion or contamination build-up in metal tanks will eventually loosen up and foul the fuel system and motor.

4) Since the ethanol component of the fuel is hydroscopic, it attracts water molecules. When the amount of water reaches a maximum limit, a phase separation occurs where the water/ethanol mixture will separate and lay in the bottom of the tank where the fuel pickup is located. This again will contaminate the rest of the fuel system and motor.  MOELLER MARINE Ethanol Info.

As far as a treatment to prevent water contamination AND remediate E-10 fuel, Starbrite’s STAR-TRON makes the strongest claims. It acts as a fuel stabilizer that prevents fuel breakdown for up to two years. It also claims to be able to reverse the effects of phase separation using an enzyme formulation.  STARTRON Spec Sheet   Also, using a water-separating filter will also contain some of these problems.

Another negative property of ethanol in fuel is that it causes an increase in fuel permeation across fuel system components such as tanks, fuel lines etc. The Environmental Protection Agency has adopted CARB fuel regulations for 2011. At great expense, Moeller Marine Products has addressed the fuel permeation issues in their fuel tanks, fuel line and accessories. The x-linked polyethylene tanks are now of a two layer composite construction and tests show that the new design will meet the new regulations. The same is true of the new fuel lines. They are grey above deck now marked as B1-15. Below deck fuel, fuel vent and fuel fill lines will continue with the ethanol resistant A2 lines currently in use. New primer balls have also been developed to meet the CARB/EPA regulations.  Moeller CARB EPA Advisory

Of course, engineering these product changes has caused a significant price hike for the end user.


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