Phase Separation in E-10 Gasoline

What is Phase Separation?

E-10 gasoline is hygroscopic (absorbs moisture from the air). If enough water is present, either from condensation or contaminated fuel, E-10 will separate into two layers of liquid: a top layer which is almost all gasoline, and a bottom layer which is almost all ethanol (up to 75%) and water (and oil, in 2-cycle fuel). This process is called phase separation, and may make an engine difficult or impossible to start.

Problems with Phase Separation

Phase separation will pull the octane booster out of the fuel, suddenly dropping 89 octane to 82 or 83. If the fuel filter is clean but the engine has no power, phase separation with octane drop has probably occurred.

The greatest potential for damage is in 2-cycle engines using pre-mix. If the engine is able to start and run, it won’t be lubricated because almost all the engine oil will have separated out of the fuel. In some cases, particularly in cold weather, an emulsion can form that can clog fuel filters and cause carburetor slides to stick.

Boats and equipment with “open” fuel systems have a breather on the tank that is always open to the atmosphere and humidity. Condensation forms every time there is a difference between the fuel temperature and the atmosphere. Over time this condensation will build up enough to cause phase separation, leaving water in the tank to cause rusting and form ethanol sludge that will clog fuel lines.

When phase separation occurs in bulk storage tanks, lower octane fuel gets distributed throughout all engines and equipment serviced by the tank.

Minimizing the Chances of Phase Separation

Use K100-G or K100-MG (with enhanced stabilizers) as on ongoing treatment to keep water out of the E-10 fuel.

Keep the fuel tank full and, if possible, close the tank vent when the equipment is not in use.