Refiners add ethanol to gasoline to increase the fuel’s oxygen content and to comply with federal law. As a side benefit, ethanol is one of a few gasoline components with a high octane rating.
But, there are significant downsides to ethanol when it comes to boat engines. Ethanol will absorb a small amount of moisture and stay in suspension within the gasoline for a while. The ethanol will absorb up to three-quarters of an ounce of water in a gallon of gas before it reaches its saturation point. Once the ethanol has absorbed enough moisture to reach its saturation point, phase separation occurs.
Phase separation means the ethanol and absorbed water drop to the bottom of the fuel container since it is heavier than the gas and oil, leaving the gasoline and oil mix to float on top of the tank. Most operators never notice water in the can when they refuel their equipment. The end result is often a carburetor ruined with rust and corrosion. These repairs can be costly and are not typically covered by warranty. Ethanol can dissolve plastic and create deposits!
Knotty Oar Marina stresses that if you choose to use ethanol fuels the layer of gasoline left floating on top has a lower octane level than the original ethanol-gasoline blend, which can result in unstable engine operation, power loss and major engine failures.
Ethanol’s affinity for water explains why so many ethanol-related problems surface in the marine industry.
Non-oxygenated gas doesn’t contain ethanol, so it eliminates corrosion problems when left in the fuel system for long periods. That makes it a great choice for engines that are stored in the off-season. Plus, it’s the fuel to use if you own an older boat that wasn’t designed for ethanol fuels.