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Ethanol Gasoline in Outboard Engines

Why can using ethanol gasoline in outboard engines be a problem? After all, it runs well in cars and should be fine for marine outboards, right? Let’s look at where the problems arise, then look at fuel additive options to protect your engine if you still decide to use ethanol gasoline.


What’s the problem with using ethanol-gasoline in outboard engines?

Ethanol is added to gasoline to raise the octane level allowing it to burn efficiently in a combustion engine. Ethanol is generally derived from corn and is considered a renewable fuel. However, the problem lies in the very physical nature of ethanol.

Ethanol prefers to bond with water rather than gasoline. Through the natural process of condensation, your boat operating in a water environment, and accidental introduction of water into the fuel system, water finds its way into the fuel tank.

Water is heavier than gasoline. If both water and ethanol gas is in the fuel tank, water will sit on the bottom of the tank – your fuel pump is also at the bottom of the tank. This is a problem, but the problem is about to compound. If there is enough water is in the fuel tank, ethanol will leave the gasoline and bond with the water potentially doubling the volume of the water in your tank. You can end up with water enriched with ethanol, rather than ethanol enriched gasoline.

This leaves the gasoline with a much lower octane level while reducing the volume of the now diminished octane gasoline by the amount of ethanol that left to bond with water. This process is called phase separation in the gasoline. The octane of your gasoline drop and, again, increases the volume of water in the fuel tank. If your fuel system experiences phase separation it can not only cause your engine to stop running but could cause serious damage or even total failure.

Additionally, in older model engines, the rubber hoses and plastics of the fuel system were not manufactured to withstand the effects of ethanol and will degrade over a relatively short time period, in some cases literally dissolving. This can lead to a multitude of hazards including fire.

However, thankfully there is a wide selection of highly effective fuel additives designed to help offset the impacts of ethanol gasoline. The following is a sampling of such products.