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Why You Should Use Ethanol in Your Marine Engine

Updated on November 22, 2017

While ethanol has been a safe way to power marine engines for years, rampant misinformation has kept many consumers away.

Ethanol: it’s more than 90 percent of gasoline sold in the U.S., but is it safe for marine engines?

In recent years, there’s been a swarm of misinformation surrounding the use of ethanol blends in marine engines. As a result, many boat owners have come to believe that ethanol mixes aren’t suitable for their marine engines when, in fact, they may be a cost-effective and safe alternative to pure gasoline.

If you care about your boat engine, here’s what you need to know about marine engines and ethanol:

Engines Have Been Running on Ethanol for 100 Years

When Henry Ford designed the first Model T, he designed it to run on ethanol. He even referred to ethanol as “the fuel of the future”. That’s because gasoline was expensive and difficult to come by, but any farmer with a corn crop could easily develop his own ethanol, saying ‘There’s enough alcohol in one year’s yield of an acre of potatoes to drive the machinery necessary to cultivate the fields for a hundred years.” Over the years, gasoline became more readily available, and transportation engines (and marine engines, as they rose to prominence) began to rely on it more exclusively.

Today, upwards of 97 percent of the gasoline sold in the U.S. contains ethanol. The most common mixture is E10, which is 90 percent gasoline and 10 percent ethanol. While it has many benefits, ethanol is most revered for its ability to lower emissions and promote fuel security.

Ethanol is made by fermenting biomass feedstocks., which is why it’s so common. The most popular type of ethanol in the U.S. is produced from corn. In addition to providing a positive energy balance, this ethanol is widely accessible and helps cut down on agricultural waste.

Another type of ethanol, cellulosic ethanol, has risen to prominence in recent years and is made from cellulose such as algae, wood, grasses, or corn stalks. While cellulosic ethanol is not as widely produced as corn-based ethanol, it results in very low GHGs and is a fantastic way to convert feedstocks that are not food-based into ethanol.

Once ethanol is produced, it is blended with gasoline at fuel terminals to make one of several popular mixtures, including E10, E15, and E85. From there, it is distributed to one of the many stations throughout the U.S. that sell ethanol blends.

Why We Use Ethanol

Ethanol is added to gasoline as an oxygenate. Because oxygenated fuels slash hydrocarbon emissions and help keep the air clean, the EPA currently mandates oxygenated additives for U.S. fuels. In addition to making fuel burn cleaner, ethanol also decreases the cost of gasoline for people using it in their marine or automobile engines. Ethanol is renewable and widely available, it helps the U.S. stretch the fuel supply to reach more consumers. This, in turn, lowers the price of gasoline at the pump.

Debunking The 4 Biggest Ethanol Myths in the Marine Industry

While ethanol has been a safe way to power marine engines for years, rampant misinformation has kept many consumers away. Here are the truths to the biggest myths surrounding ethanol in marine engines:

1. Ethanol-Enhanced Fuel Does Not Lose Octane More Rapidly Than Standard Gas

For people who intend to store their engines during the winter, concerns about octane loss can be enough to prevent the use of ethanol. For years, people have believed that ethanol loses octane more quickly than traditional gasoline. This is a myth, according to BP Global Fuels Technology in a report published by BoatUS, ethanol loses octane at roughly the same rate as standard gasoline.

With this in mind, storing ethanol fuel in your boat’s engine over the winter will not damage the engine. That said, it is always a good idea to add fuel stabilizers to gas tanks whenever an engine will be inactive for a long period of time, no matter what type of fuel you’re using.

2. Ethanol Does Not Attract Water

While ethanol is hydrophilic, which means it holds water, it does not draw water from the atmosphere surrounding it. The truth is that all fuels are susceptible to water collection, and condensation increases when tanks are less than half full.

While pure gasoline doesn’t hold much water, BoatUS points out that E10 can hold about half of one percent of water by volume. When it does, the water molecules will dissolve in the fuel mixture. Even if your E10 retains this much water, though, it will bypass your engine’s water separation mechanism and burn in the engine without causing harm.

Want to take extra precautions? Consider using a fuel filter. Fuel filters trap harmful substances to keep your engine clean and running well. A good filter is especially important if you’re just transitioning to ethanol-blend fuels because ethanol will essentially clean out years of buildup in your tank.

3. You Do Not Need Additives to Prevent Separation

In an attempt to prevent phase separation, some people have turned to additives. Unfortunately, no additive on the market, no matter how good, will resist a large amount of water. As such, boat owners are just advised to keep their tanks filled and dry to prevent condensation. When it comes to water in marine fuel, an ounce of prevention is worth a pound of cure. It is important to remember all gasoline degrades over time, whether from evaporation, contamination, or oxidation.

Is Ethanol Safe in Older Marine Engines?

While ethanol is safe for modern marine engines, it’s important to pay special attention to marine engines built before about 1991. While it may seem like few boats that old are still in operation, it’s important to remember that marine engines are some of the oldest in the country. While cars don’t often run for decades, boats do, which means that many engines currently in operation may well predate the rise of ethanol-blended fuels.

Because these engines were designed to run on standard fuels, they may need some special attention to accommodate ethanol blends. Most of this attention should be paid to the hoses within marine engines. In older engines, hoses are typically constructed of rubber or plastic. In more recent years, though, hoses are made to abide by a new standard, known as SAE J1527. Hoses constructed to this standard are meant to hold up to ethanol.

If you own a boat built before 1991, you won’t have to do much to ensure it accommodates ethanol. As a general rule, fuel hoses should be replaced every 10 years. Any hose 20 years old or older is no longer safe. If your hoses are original, be sure to have them replaced with more modern hoses before running any fuel through your engine.

Common in older engines, plastic and rubber components can get brittle which can cause problems within the engine. Often ethanol gets the blame for these failing parts when older materials are the real issue.

The Case for Ethanol in Marine Engines

All engines, big and small, are certified and warrantied for E10 use.

Ethanol is a very common component in gasoline, and ethanol blended fuels are everywhere. While many boat owners have some reservations about running ethanol blends through their engines, it’s important to remember that ethanol fuels are actually quite safe, especially for newer engines.

While the transition to ethanol-blended fuels in an old engine can sound laborious, it is straightforward and easy to overcome. Boats with old components should have their hoses, gaskets, and seals replaced, while tanks for small engines that sit for long periods should receive a fuel stabilizer. Additionally, all fuel tanks should be kept as full as possible at all times so as to prevent condensation.

Once you’ve resolved those minor concerns, there’s no reason not to run ethanol blends in your marine engine. In the words of Mercury Marine, a leading marine engine company, “After the transition period from E0, E10 may actually be a superior marine fuel as it tends to keep low levels of water moving through the fuel system, keeping the system ‘dry.’”

In fact, the fastest boats on the water today, like Don Onken’s 51-foot Mystic Powerboats catamaran, are using a mixture of 85 percent ethanol to break world records.


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