Ethanol and Boat Fuel: Stay Vigilant

If you’re new to boating and are looking at used boats to buy, you might not be aware of the running battle boaters have been waging with ethanol-based fuel for years. Ever since the widespread introduction of ethanol-blended fuel in 2006, many boaters eith gasoline-powered engines have experienced performance problems directly related to the added ethanol in gasoline. Boats with fiberglass fuel tanks are particularly susceptible. Read on.
A combination fuel filter and water separator will collect water in a clear reservoir at the bottom. Keep a close eye on that reservoir and drain anywater out right away
A combination fuel filter and water separator will collect water in a clear reservoir at the bottom. Keep a close eye on that reservoir and drain anywater out right away

What is Ethanol, and Why Does It Cause Problems?

Ethanol blended gasoline was introduced in the United States as a renewable fuel alternative that would help reduce dependence on foreign oil. Because ethanol is derived from corn, the production and refinement of ethanol supports the agricultural industry and rural communities. Burning ethanol gasoline also produces 3 to 4 percent fewer greenhouse gas emissions than pure gasoline. The growing adoption rate of ethanol has escalated in recent years and use is even mandated in some states.

Although ethanol blended gasoline has caused little to no issues on cars, the use as marine fuel has caused quite a few problems for boat owners. The problems are mainly linked to the fact that ethanol is a solvent that can react with boat fuel tanks, fuel filters, and carburetors, causing an engine-stopping sludge. The ethanol solvent interacts with water that forms from condensation that commonly gathers in a partially full fuel tank. Because ethanol is a hygroscopic, it attracts and attaches to any water in a fuel tank, creating a clogging sludge that is problematic for fuel filters, carburetors, and engine parts.

Fiberglass fuel tanks typically found in older boats are made with a resin that can also react negatively with ethanol-blended gasoline. The sludge build up can cause performance issues, ongoing repair or maintenance issues, and can even ruin an engine.

Ethanol Related Boat Engine Problems

The use of ethanol blended gasoline can wreak havoc on your boat engines if not carefully monitored. To limit the impact of ethanol problems in boat engines, consider these precautions:

  1. Don’t let ethanol gasoline sit in fuel tanks. Ethanol gasoline sitting too long in a fuel tank is more likely to absorb water and cause problems. Use fuel within 90 days and refuel often to prevent problems.
  2. Keep up with maintenance. Be sure to change fuel filters and maintain a clean carburetor to limit sludge build-up caused by ethanol in your boat engine. At every fill-up, use a good fuel additive.
  3. Address issues quickly. When performance problems persist, such as a continually fouled carburetor, consider taking the proactive measure of draining a fuel tank and refueling. Cleansing your fuel tank of any gasoline impacted by ethanol may save you from bigger issues like a destroyed boat engine. For more on this see How to Get Rid of Bad Boat Fuel.
  4. Choose ethanol-free fuel. You may have options for avoiding ethanol gasoline altogether. Some marinas now offer ethanol-free fuel or fuel with additives that may reduce the impact of ethanol in gasoline.
  5. Fuel your boat at marinas. Don’t risk fueling your boat with a higher level of ethanol if E15 becomes available at gasoline stations on land. Fueling your boat at a marina will be safer because E15 is not approved for sale at a marina.

Concerns over Increasing Ethanol from E10 to E15

In 2010 the EPA approved an increase of  ethanol in gasoline from 10% (E10) to up to 15% (E15). Availability is not widespread, and the EPA has stipulated that E15 cannot be used  in a variety of vehicles and machinery, including boats. Still, the National Marine Manufacturer’s Association (NMMA) and other boating industry groups have warned that “there is significant risk of consumer confusion and misfueling.” Experts are concerned that even though E15 may not be offered at your local fuel dock, there are many owners of smaller boats who choose to purchase their gasoline on land at standard gasoline stations. Also, the marketing of E15 as a lower-cost fuel may be attractive to boat owners who aren’t informed about the potential impact on their boat’s fuel systems and engines.

So be vigilant. With ethanol, an ounce of prevention is worth several pounds of cure.



Constant vigilance and regular maintenance of fuel filters against water and sediment in fuel systems can prevent expensive engine problems and tank corrosion.
Beware of Foul Fuel in Used Boats
Category: Buying

When you're thinking of buying a used boat, any extra time you or your surveyor take to make sure of...

Volvo-Penta's new treatment should be a potent ally in the war against water in marine fuel.
Ethanol’s Worst Enemy
Category: Boat Engines
Volvo-Penta introduces a new additive to combat the destructive nature of alcohol.