In the United States, the amount of ethanol allowed for use in gasoline is federally controlled by the EPA (Environmental Protection Agency). Based on these regulations, the current maximum allowable ethanol content in gasoline is 10%. In conjunction with this mandate, most outboard manufacturers â€“ including Mercury Marine â€“ have designed their outboards to tolerate up to 10% ethanol. Unfortunately, some of the fuel samples Mercury has tested that were taken directly from the engineâ€™s fuel system have actually shown ethanol content as high as 30%, or three times the maximum allowable amount. This is most likely the result of phase separation that has occurred inside the boatâ€™s fuel system (not necessarily from the gas pump having higher ethanol content).
Phase separation essentially means that the ethanol in the fuel has attracted water (usually already present from condensation and/or other sources) into the fuel mix. When the right amount of water enters the mixture, most of the ethanol and water will tend to separate from the fuel (into a different â€œphaseâ€) and drop to a lower level or layer inside the tank (water is heavier than fuel). If this layer of concentrated ethanol and water is drawn into the engineâ€™s fuel system, significant damage can occur. Further, the level at which phase separation occurs is determined by a number of variables, one of which is the temperature of the environment. This may help to explain why some regions of the country may be more affected by ethanol than others. Mercury Marine believes this higher ethanol exposure has caused product failures in fuel system components on two-stroke and four-stroke product.
Ethanol has very different solvency behaviors than gasoline and is a proven contributor to the deterioration of certain rubber and/or plastic components and electrical potting compounds. Mercury is aware of this potential and is constantly working to implement material improvements to better withstand the effects of ethanol. One such improvement in place on all 75-115 hp four-strokes since 2006 and Verados since June 2007 (most easily identified by the polished chrome graphics package) is an improved float switch in the fuel supply module that ensures the integrity of the switch itself, even when exposed to higher ethanol concentrations. This change alone should address the majority of ethanol-induced product failures within the fuel system.
Mercury continues to monitor the ethanol situation worldwide and makes every effort to upgrade materials as necessary to ensure the continued reliable, durable operation of all of its outboard products.
For more information on ethanol, including what you can do to minimize its effects on your outboard, please review Mercury Marineâ€™s comprehensive Ethanol FAQ document at http://www.mercurymarine.com/service...qs/ethanol.php