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Ethanol FAQ

What is Ethanol?

Ethanol is a clean-burning, high-octane fuel additive that is produced from renewable sources. At its most basic, ethanol fuel additive is denatured alcohol, produced from crops such as corn or sugar cane. Adding ethanol to gasoline "oxygenates" the fuel, adding oxygen to the fuel mixture, so that it burns more completely and reduces polluting emissions, such as carbon monoxide, hydrocarbons, and oxides of nitrogen. The U.S. Environmental Protection Agency (EPA) requires the use of oxygenated gasoline to improve air quality. Many regions use Methyl Tertiary-Butyl Ether (MTBE), but it is gradually being eliminated, due to its contamination of ground water systems and soil through leaking underground storage tanks.

Any amount of ethanol can be combined with gasoline, but the most common blends are:
E10 - 10% ethanol and 90% unleaded gasoline
E85 - 85% ethanol and 15% unleaded gasoline

It is important to note that modern engines can use E10 with no modifications. E85 is for use in a flexible fuel vehicle so some people confuse "ethanol" with the blend of 85% ethanol and 15% gasoline. Currently, there is not a marine engine on the market that will work with E85.

What is the Problem?

Ethanol is a hygroscopic substance, meaning it attracts water. The presence of ethanol in fuels may contribute to decreased fuel surface tension, which in turn may promote increased fuel tank condensation from air moisture.
Another problem with the introduction of ethanol comes from the mixing of old MTBE gas with the ethanol gasoline, especially if water is present in the fuel. If a significant amount of water is present in a fuel tank with gasoline that contains ethanol, the water will be drawn into the fuel, until the saturation point is reached, resulting in the three-component mixture of water + gasoline + ethanol. It is at this point that phase separation may occur. Phase separation is a process that can cause most of the ethanol and water to separate from the fuel and settle to the bottom of the tank. This leaves your gasoline with a significantly reduced level of ethanol in the upper phase, while the lower phase of the gas would contain a gelatinous mixture of water and ethanol. If the lower phase is large enough to reach the fuel inlet, it could be pumped directly to the engine and cause significant problems.
Ethanol is also a very good solvent, which allows it to loosen rust and debris that might lie undisturbed in fuel systems. Since ethanol has such good solvent properties, it can more readily remove plasticizers and resins from certain materials that might not be affected by gasoline alone. Loose debris will plug filters and can interfere with engine operation.

Ethanol is being introduced to my area. What should I do?

There are a lot of stories centering on the introduction of ethanol into the marine environment, but not all are true. Most all problems can be avoided with proper preventive measures.
Before ethanol is introduced to your fuel tank, ask your boat manufacturer if any special precautions should be considered with the use of fuel containing ethanol. If there are no compatibility issues with your boat/engine manufacturer and the use of ethanol, then you may find the following guidelines helpful in your transition.

Before you fill-up with ethanol-based gasoline, empty all of the old MTBE fuel from the tank to help avoid any ill effects of mixing the two fuels.
Check for the presence of water in the fuel tank. If any is found, remove all water and dry the tank completely.
Use a good quality water separating fuel filter and carry several spare cartridges for it. The Moeller Clear Site fuel filters (Overton’s item numbers 75846, 75848, 75850) are a great choice. Your first few tanks of the new ethanol based gasoline, may loosen and remove contaminates into your fuel system. This may cause an initial bout of clogged fuel filters, but this will pass as your system is cleared of these contaminates. As a precaution, carry a few extra filters, in case filter plugging becomes a problem during boating.
Twice a year inspect your fuel lines, fittings, and tanks for any signs of leaks, cracking, wear, etc. Replace worn components to insure safe boating.


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