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Do I Really Need To Use Ethanol Free Fuel In My Boat?

Over the past several years, ethanol has gotten a real bad rap with recreational boaters.  Stories of engine damage and getting stranded out on the water have been told time and time again.  One group says that boaters should stay away from it while another group says it is perfectly fine to use.  Who is telling the truth?  Well, it depends.  Let’s take a look at how we got here and what is really going on.

In 2005, the Renewable Fuel Standard Act was passed that required a certain amount of renewable fuel to be used along with the fossil fuels that we had already been using.  This was done to reduce the amount of pollution that fossil fuels create.  Ethanol was chosen because it can be made from a renewable resource that is readily available in the US.  Gasoline powered cars and trucks had no problem with the switch at all, but we cannot say the same thing for the boats.  To understand this, let’s take a look at some of the characteristics of ethanol.  

It is important to know the characteristics of ethanol fuel before using it in your boat.

1.        Ethanol Attracts Water – Over time, ethanol will absorb water, even directly from the air.  When this happens, the fuel goes through a process called phase separation.  The heavier water laden ethanol sinks to the bottom of the tank while the rest of the fuel remains above it.  As you can imagine, this combination of ethanol and water does not burn well and it can cause other problems such as sludge and corrosion.  To top it off, the remaining ethanol free fuel at the top is now of a lower octane level than when it was fresh. 

Why this is an issue for boats?  - With boats, there is moisture all around and plenty of it to be absorbed.  Boats are also more likely to sit for longer periods of time between uses, especially during the off season.  During that time, the ethanol in the fuel sitting in the tanks has a lot of opportunity to soak up moisture.  Since we typically drive our cars several times a week or more, the fuel does not remain in the tanks long enough for phase separation to occur.  You probably have also heard of complaints with lawn equipment experiencing issues with ethanol fuels.  This is primarily because like boats, lawn mowers, weed whackers and other gas powered lawn equipment may also sit for long periods of time between uses.   

What can I do? – Of course, you could just avoid using ethanol fuel altogether but understand that the fuel is not what can damage your engine.  It is what happens if you let unused fuel sit for too long in the tanks.  If you are the type of boater that uses your boat once every month or so and not at all in the winter, then you may want to stick with ethanol free fuel.  However, if you use your boat constantly (like I do), you should not have any of the issues related to phase separation.

Phase separation can occur if ethanol fuel is left unused for too long.

2.        Ethanol is a Solvent – This may sound good at first, because it means that it cleans the gunk out of your fuel system.  To an extent, that is true, but if you do have a dirty fuel system and you all of a sudden switch to ethanol fuel, you could end up with clogged fuel filters.  If that happens at the wrong time, you may find yourself stranded.   

What can I do? – Having a clean fuel system is a good thing.  Being stranded is not.  If you suspect that your fuel system is dirty and you want to use ethanol fuel, make sure you have extra fuel filters.  Don’t wait for there to be an issue before changing them.  Eventually, as the gunk is cleaned out, you will be able to go back to a regular schedule for changing filters.

3.        Ethanol and Fiberglass Fuel Tanks – Remember that ethanol is a solvent.  If your boat has fiberglass fuel tanks, ethanol in the fuel can react with the resin in the fiberglass and start to break it down.  This ends up clogging up your fuel system and engine and that is definitely not a good thing.  Newer boats do not have fiberglass tanks but some older boats do.  If you have an older boat, make sure you know what your fuel tanks are made of before fueling up with ethanol fuel. 

What can I do? – If your boat does have fiberglass tanks, DO NOT use ethanol fuel at all!

One more thing to keep in mind is that even if you have determined that you are clear to use ethanol fuel in your boat, it is still not recommended that you use fuel with more than a ten percent blend (E10).  In many states, E15 is now being sold and E85 has been marketed for quite a while for flex fuel vehicles.  New boat manufacturers have agreed that anything up to 10 percent is fine and will not void new boat warranties but using fuel with a higher percentage of ethanol is not recommended. 

So what does the future hold?  Will we have to deal with this ethanol debate forever?  Maybe not.  A suitable replacement for ethanol has been found, tested and approved.  It’s called Biobutanol.  Like Ethanol, it is a type of alcohol but it does not absorb water and it is not as strong a solvent as ethanol.  It also can be made from agricultural waste products like corn stalks and wood chips and it has more energy than ethanol does.  It tested well in marine engines and in 2015, it was approved by NMMA.  
Biobutanol is an alternative to using ethanol because it does not come with some of the negative side effects.

So why are we not using it?  To put it simply, it is because ethanol producers have powerful lobbyists in Washington who will fight against the acceptance of any fuel that is not Ethanol.  That being said, there are a handful of gas stations and marinas on the east coast that sell gasoline containing Biobutanol instead of ethanol.  Some blends of this fuel are referred to as B16 because it contains 16 percent Biobutanol.  If you see a station that sells B16, consider supporting them and help spread the news.

Happy Boating

Captain Frank
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  1. i USE 100% GAS because it is available at both The Marinas and Gas Stations around Dale Hollow Lake in Kentucky and Tennessee

  2. My 115 Honda is rated to use 86 octane, but it’s my preference to use 93 octane with a stabilizer.

  3. not if you don't mind breaking down

  4. Umm, yes. I didn't even read this. I thought everyone knew Ethanol was a big no-no.

  5. Very good article, except for the part about fiberglass tanks. There are different reasons that fiberglass tanks are made from. The older boats; Hatteras, Bertram...were the 2 big companies that used polyester resin to make their gas tanks. Those tanks, basically melted from the inside out and gummed up and ruined valve trains in engines and caused gasoline to lay in bilges. Modern fiberglass tanks are made with vinylester resin. This type of resin is the same type used in underground storage tanks.. I had a vinylester resin tank made and it’s been in use since before the Ethanol introduction.

  6. The really sad part about the ethanol government scam is that its energy production cost is more than you can ever get out of it. Also, fuel efficiency is reduced so more fuel is burned, thus polluting more. Can anyone point out to me something good about ethanol. Note: in some other countries it is illegal to grow corn for conversion to ethanol.

    1. Yes, but go explain that to the Iowa farmers!

    2. It was supposed to be voted on in 2014 to quit making ethenal. I don't know what happened

  7. Ethanol in fuel is nothing more than a farm aid program.

  8. Quo boards are a type of visual aid that can be used to communicate information or ideas. They are often used in presentations or workshops to help participants engage with the material being presented. Quo boards typically consist of a series of images or illustrations, with each image representing a different concept or step in a process. Participants can then use the quo board to discuss the information being presented, or to brainstorm ideas related to the topic at hand.


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