Ethanol in Pleasure Boats
Recently, we have had many questions about the effect that ethanol has on marine engines.
The government's decision to include this chemical in petrol is a perfect example of unintended
consequences. Many engines that use fuel injection pumps are now beginning to operate poorly
(stalling, skipping, and starting hard) and often make a high-pitched squealing sound.
Manufactures of the fuel injection pumps that Volvo Penta uses, have had particular problems
with ethanol and some poor boat owners have had to replace pumps multiple times.
While carbureted engines are not affected as dramatically, fuel left in the carburetors for any
length of time leaves varnish-like deposits that can cause problems (especially at higher
speeds) and require the pump to be disassembled and solvent cleaned. These are just some of
the issues.
Fuel suppliers are increasingly offering an ethanol and petrol blend known as E10. E10 fuel
contains 10 percent ethanol and 90 percent petrol, and is acceptable for use in all fuel-powered
automobiles. This doesn't mean that E10 is a welcome change for the boating industry,
however.
E10 may be a safe, alternative, bio-fuel for your car or truck, but, in the setting of a marine
engine, E10 poses a unique set of problems. Fuel mixtures containing ethanol have behaviors
that can be harmful to your marine engine. The most important of which is how ethanol interacts
with water and other compounds commonly found on your boat and in your engine.
E10 supposedly creates fewer emissions and reduces reliance upon foreign oil. Beyond that,
ethanol replaces an additive called MTBE (Methyl Tertiary-Butyl Ether), a potentially
carcinogenic substance that oxygenates petrol as well as increases its octane. As of 2008, 25
states in America created laws banning the use of MTBE enhanced petrol. Since that time,
ethanol has become the preferred petrol additive.
50 Times More Water Absorption
Ethanol is hygroscopic, meaning that water molecules have a natural attraction to it. Because of
its chemical composition, ethanol is predisposed to both absorb and retain water. Ethanol will
absorb over fifty times more water than petrol alone. This might be beneficial in the context of
sponges or bath mats; however, the combination of fuel and water is disastrous to the fuel
system of a boat. Petroleum products, on the other hand, do not blend with water. At 21
degrees Celsius, traditional petrol will only absorb 150 parts of water per million (ppm). E10 will
absorb a staggering 6,000 to 7,000 ppm at the same temperature.
Since ethanol molecules uniformly distribute throughout the petrol molecules, when ethanol
performs its peculiar feat of absorption, it effectively distributes water throughout the entire
volume of liquid fuel. The clumped-up ethanol and water molecules then settle to the bottom of
the fuel tank because they have a higher density than straight Petrol. The name of this process
is phase separation. This is why people shake the can. Interestingly enough, it only takes a
small amount of water to produce phase separation in E10-to the tune of just 12.5cc per litre of
petrol. Addressing the issue of phase separation is essential because it has the potential to
wreak havoc with a boat's fuel system. Unlike automobiles which have closed fuel systems (why
you hear psst when you remove the fuel cap), boat engines, under regulations, cannot have
closed systems and must be vented. This means that not only does ethanol absorb water, but it
keeps getting new sources of water from the water vapor in the air.
Besides being hygroscopic, ethanol is also a solvent. A solvent is a liquid that can dissolve
another substance, and ethanol is a very powerful solvent at that. It is capable of eating through
resins, rubbers, even metals. This puts your fuel system (lines, tanks, filters), as well as your
engine at risk. When you cut apart failed fuel injection pumps there is a fine black powder. This
powder (similar to very fine baby power) is from the internal coating of the pump installed during
the manufacturing process. The solvent in the ethanol breaks the coating down. When you hear
the high-pitched squealing, it is the fuel being forced by and around the powder trapped at the
end of the pump. If you continue to run your engine, you can break down the powder even finer
and push it out of the pump into the fuel injectors and ruin them.
If you own a fiberglass fuel tank, ethanol can dissolve the resin inside the tank. This
incorporates contaminants to your fuel system in two ways. First, by introducing dissolved resin
particles into your liquid fuel; second, by chancing that fiberglass particles loosened by the
erosion will break free and get into your system. Outside of the fuel tank, ethanol can destroy
fuel lines, fuel kits, and other soft engine parts that aren't resistant to its effects. This can
sometimes be first noticed for those who own outboards with a fuel primer bulb.
As if being a solvent and hygroscopic weren't enough, ethanol is also a potent degreaser. This
means that if anything is clinging to the inner-working of your engine, be it grease, sludge, dirt,
rust, or other type of infiltrate, ethanol will work its magic and release it into your engine where it
will be distributed to parts like your valves, carburetor, filters, and injectors.
Ethanol also causes galvanic corrosion because of its affinity for water. Once ethanol has
absorbed water that gets into the fuel system, it creates an environment ripe for corrosion. Even
aluminum isn't resistant to the effects of the water that has been absorbed into the E10 and will,
over time, erode the surfaces of aluminum parts. Water and aluminum produce aluminum
hydroxide. Aluminum hydroxide in conjunction with heat produces aluminum oxide, which just
happens to be one of the abrasive ingredients found in sandpaper.
3-4% less fuel economy
Two other issues of importance are reduced fuel economy and shelf life woes, both of which
can increase your fuel costs. A litre of ethanol contains less energy than a litre of petrol. The
result is lower fuel economy. Simply put, it takes more E10 to produce the same amount of
energy as a similar amount of straight petrol. Australian V8 Supercars freely state this when
describing their fuel strategies. Estimates often give the fuel economy reduction to be around 34 percent per litre. This problem compounds itself once phase separation has occurred. As soon
as ethanol absorbs the water, it leaves two unhealthy layers of fuel in your tank, a contaminated
bottom layer and a low octane top layer. Low-octane fuel reduces engine power and
performance.
Up to 90 Days
E10 doesn't perform well over time, either. While straight fuel will often last years if properly
stored, experts recommend not storing E10 in your fuel tank for more than 90 days. And that
figure is the very upper end of the spectrum. Some sources will even state that its death-clock
starts ticking at the two-week date. If you're a commercial boater, this may not be a concern,
however pleasure-boaters beware.
Fuel System Preventive maintenance
The part of your boat that is most vulnerable is your fuel system. Here is a list of fairly
inexpensive ways to alleviate fuel system issues.
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Don’t use E10.
Replace old rubber fuel line hoses with modern barrier lines. This will prevent leaks and
dislodging particles.
Always have spare fuel filters on-hand. Nothing spoils the day like a clogged filter,
having one on-hand will prevent a lot of wasted time. Many people change the fuel filter
once a year. If you use your boat a lot then, paradoxically, you might be able to have a
single filter change as the fuel is used up quickly, but if the boat sits around a bit unused,
you might want to change the filters again after the wet season.
Install a second in-line water-separating filter between your fuel tank and your engine.
This will add another layer of protection to your system. Always hire an authorized
installer to perform this type of work.
You might want to make sure you have a spare raw water impeller onboard and store it
in a cool dry place. Sea water sucked in by the raw water pump sit in the pump when the
engine is not running. The impellers can get brittle and fail if the vessel is not used for
long periods.
It's generally advisable to plan ahead so that your boat is stored with a minimum quantity
of fuel.