Yamaha Outboards Fuel Recommendations

Yamaha, makers of marine outboard engines, maintains a section on their website for frequently asked questions concerning the use of ethanol blended gasoline.

Are Yamaha engines compatible with E10 fuel?

All current models as well as most engines built since the late 1980’s have been designed with fuel system components that are tolerant to fresh fuel containing ethanol up to 10% (E10). Outboard fuel systems can still be affected by: water, dissolved gum, varnish, corrosion particles, and dissolved resins that E10 fuel has cleaned from the distribution system and your boat’s fuel tanks.

Source : Yamaha Outboard FAQs

Ethanol Phase Separation

The EPA published a report in 1995 that deals with the issue of phase separation in oxygenated fuels. The primary oxygenates discussed in the report are ethanol and MTBE.

Phase separation occurs when the water content reaches the maximum amount that the gasoline blend can dissolve, any additional water will separate from the gasoline. If the only source of water is from moisture in the air, phase separation is unlikely to occur due to the length of time required.

For example, at a constant temperature of 100 degrees F and relative humidity of 100%, it would take well over 200 days to saturate one gallon of gasoline in an open gasoline can (assuming the only source of water is water vapor from the air). Water absorption from the air is far slower at lower temperatures and humidities. (At a temperature of 70 degrees and relative humidity of 70%, it would take over two years to saturate one gallon of conventional gasoline in the same gasoline can.) Again, oxygenated gasolines can hold more water than conventional gasoline, and would therefore take much longer to saturate with water.

Source : Water Phase Separation in Oxygenated Gasoline

Mercury Marine's Fuel Recommendations

Mercury Marine is a leading manufacturer of outboard engines and stern drives for boats. They maintain a section devoted to ethanol blended fuels on their website.

Some of the issues that I have seen discussed in the media latley with regards to ethanol's use in boats are addressed.

Are Mercury engines compatible with ethanol fuels?

The fuel-system components of Mercury engines will withstand up to 10 percent ethanol in gasoline - the maximum level currently allowed by the EPA in the U.S.

How does ethanol affect my fiberglass fuel tank?

Fiberglass tanks manufactured prior to 1991 may not be compatible with gasoline containing ethanol. It has been reported that, in the presence of ethanol, some resins may be drawn out of fiberglass and carried into the engine where severe damage could occur. If an older fiberglass tank is used, check with the manufacturer to determine if gasoline with ethanol can be safely used.

Are older fuel lines prone to failure? What about gaskets?

During the 1980s, many rubber components for use in fuel systems were developed to withstand exposure to fuels containing ethanol. If rubber components in a fuel system are suspected to be of this vintage or older it may be advisable to replace them with newer ethanol-safe components before using fuels containing ethanol. Check with the manufacturer for advice or frequently inspect these fuel-system components for signs of swelling or deterioration and replace if problems are noted.

Source : Mercury Marine

Evinrude Outboard's Fuel Recommendations

Evinrude is a leading maker of outboard motors for boats. In the Frequently Asked Questions section of their website they state that fuels containing up to 10% ethanol are allowable.

Q - I live in an area where they only sell oxygenated fuels. Will this hurt my motor?

A - Oxygenated fuels should not hurt motors. Motors can tolerate up to 10% alcohol in fuels, which is the maximum allowed by law in the United States.

Source : Evinrude