According to a warning by Yamaha Motor Corporation, ethanol gas is the largest cause of trouble with marine engines these days. If you’re unfamiliar with ethanol, it’s being added to the majority of today’s fuel supply as an oxygenate to help reduce emissions. The problem with ethanol gas, which is basically 200 poof grain alcohol, is that it’s also a powerful solvent that can loosen debris in your fuel tank and all the tanks and lines it was in before it got to you. Once in your outboard, this dirt can cause everything from running issues to a no-start, no-run condition.
E10 is the common ethanol-gas blend found at most gas stations around the US. “E10” indicates the ethanol-to-gas-ratio (10% ethanol, 90% gas). Higher ethanol blends like E15 (15% ethanol, 85 gas) and even E85 for flex fuel cars (85% ethanol, 15% gas) are also available. Running your car on a low ethanol-blend fuel, such as E10 or E15, isn’t a problem since the car is used almost daily, your boat is a different story altogether. Most boats aren’t out on the water every day, they often sit unused for weeks or even months at a time, giving the solvent a chance to go to work on the fuel system.
Ethanol is alcohol, and alcohol is “hygroscopic,” which means it attracts water molecules. Since nearly all boat fuel tanks are vented to the atmosphere, water will collect in your fuel. When the concentration of water molecules in your fuel tank reaches just 1⁄2 of 1%, the water molecules will bond with the alcohol and sink to the bottom, where your fuel pick up is. This process is known as “phase separation” and depending on the amount of water ingested into your outboard, can result in everything from running problems to catastrophic damage.
Plugged high pressure fuel filters are a common ethanol related problem. This picture shows a filter covered in aluminum particles from an older aluminum tank that had its oxidation removed by the ethanol solvent.
Ethanol is also known for delaminating fuel lines. This picture shows how a line breaks down. As they deteriorate, pieces of the fuel line will actually travel to the engine and plug up the fuel filter.
If you have to use an ethanol blend fuel, be sure not to use a blend higher than E10 (10% ethanol) in your boat. If you have a newer boat, there will likely be a warning sticker next to your gas tank with a similar warning. There’s a big difference between E10 and E15 and you could end up destroying your boat’s engine and voiding your warranty if you use E15.
If you have to use E10 gas, make sure you have a high-quality (at least 25-micron) marine fuel-water separator filter installed in your boat’s gas line. this filter keeps water and debris out of your engine. Check the filter and replace it regularly, and if you see a lot of plastic or fiberglass “gunk” building up in your filter, take your boat to a mechanic immediately since this likely means you have fuel system parts that are being worn away by the ethanol.
Finally, make sure to completely fill your gas tank if you’re not going to be using your boat for an extended period of time. A half-full tank of E10 is likely to end up absorbing a lot of water from the outside air to the inside of your gas tank. If the gas tank is full, there isn’t anywhere for the air to go. Also remember to add a marine specific fuel stabilizer to your tank of ethanol gas as it will help prevent water absorption and phase separation.
Learn more about ethanol and what you can do to fight more of it on BD.