The Perils of Ethanol
  |  First Published: October 2008

While ethanol is fine in a modern car and reduces our reliance on precious petrol, some boat owners using ethanol blended fuel are about to experience melted fuel tanks, leaks and damaged engines.

That’s why all of the four oil companies I called recommended that I didn’t use ethanol in any boat.

Outboard Engine Distributors Association chairman David Heyes said that his members were concerned at the use of ethanol in outboards. He said that while almost all modern outboards can at least tolerate E10 (10% ethanol), the outboard industry was very concerned with the potential damage to fuel systems and especially for the safety of boat owners.

The risks for boat owners come from two key characteristics of ethanol. It’s a powerful solvent and it doesn’t stay mixed with petrol, meaning it has a very short shelf life.

E10 fuel is available at many servos at 3 cents a litre cheaper than regular unleaded. Despite this discount it’s still less than 2% of total fuel sales. The option we fear is compulsory levels of ethanol in every litre sold.

NSW has had a 2% ethanol mandate since 2007 and Queensland has announced a 5% mandate from 2010, which may affect fuel distribution into northern NSW.

Ethanol blended fuels have been used in the US for some years and the risk to boats is well documented. That means that boat builders here need to stop using fibreglass and even aluminium tanks to avoid future liabilities.


There are no dollars to be saved by using E10 at today’s prices. Ethanol has a heating value of 23.5 MJ/L, or more than 30% less than petrol. That means that a 10% mix will lose about 3% in fuel economy.

So if unleaded fuel is $1.70 a litre, E10 has to be under $1.65 just for the buyer to break even. Currently the price difference is closer to 3 cents – hardly a bargain.


Ethanol is going to liberate dirt and residue in your fuel system that you never knew existed. In 2007 Shell had to shut down its ethanol sales for a period because the new fuel in old tanks just kept releasing sediments and blocking up filters.

Boaties will experience the same blocked filters. So if you end up using ethanol, plan for a filter change after the first tank and carry a spare.

Even the best filters won’t stop every nasty. Some chemicals become dissolved and pass though the filters before being redeposited inside the engine.

Boats with fibreglass tanks are most at risk. Ethanol soon dissolves the resins, eventually weakening the structure and inviting leaks.

That also means any fuel spills around the filler cap can cause permanent damage to the gelcoat and need to be wiped up and washed off immediately.

Boat USA conducted tests on 1967 and 1970 Bertrams that showed signs of engine and fuel system damage. They found black material on an intake valve which indicated esters, ketones and polyester – the fibreglass fuel tanks and perhaps fuel lines were dissolving and these chemicals were passing straight through the filters and into the engines.

The fuel in the tanks showed styrene, a component of polyester resin. The tanks showed ‘aggressive degradation’ and had lost 40% of their strength.

Some boat builders have been planning for this day. Greg Haines, of Haines Signature, says their fibreglass boats all now have appropriate plastic tanks.

Aluminium tanks are reported to be at risk of corrosion because ethanol makes fuel more conductive, meaning only approved plastic and quality stainless tanks will meet future requirements.

The US introduced fuel tank standards for ethanol years ago. Australian regulators need to catch up.

Hoses and gaskets incompatible with ethanol can also be damaged. If your boat is more than six years old, or has been left outside and exposed to UV, start budgeting for a complete fuel system refit if you use E10.


Ethanol absorbs moisture. Beyond 0.5% absorption, the saturated ethanol sinks to the bottom of the tank and no amount of stirring will remix it and no additives will fix the problem.

At the top of the tank we are left with straight petrol, which sounds great until we realise that the ethanol was our octane booster. So the first sign of separated fuel may be pre-ignition or pinging as the octane in our remaining fuel drops from, say, 91 ron to 88 ron.

As the saturated and separated ethanol in the tank builds up over subsequent fills, it eventually reaches the pickup, when a 100% dose of ethanol goes through the engine. Systems and fittings designed to cope with a maximum of 10% ethanol face real damage and dangerous leaks.

Moisture will always collect in fuel tanks so the ethanol has plenty of water to absorb. Humid air is drawn in though the tank breather and on the next cool morning condenses in the tank and is immediately attracted to the ethanol.

Light aircraft pilots know this phenomenon. Their pre-flight checks include draining a small amount of fuel from the bottom of each tank, along with at least a few drops of water.

Boats parked in a driveway or left on a mooring will suffer condensation in fuel tanks so this ‘phase separation’ is inevitable and the only cure is to empty the tank and clean out any ethanol and water in the bottom. That means opening up the tank, not just pumping it empty through the fuel pickup.

Disposing of this fuel is a real problem, with councils offering very restricted collections.

The traditional solution to condensation is to keep the tank full, leaving little space for moist air, but that’s not always desirable when your next boat trip may not be for a month. E10 has a shelf life as short as two weeks because the ethanol evaporates very quickly.


BP, Shell and Caltex all advise boat owners not to use ethanol mix fuels in boats. They say that is mostly because ethanol has a dramatically shorter life, especially in a marine environment.

To reduce moisture accumulation, tanks must be kept full so there is less space for condensation. On the other hand, ethanol blends should be kept for no longer than two weeks.

Keeping the tank full yet regularly turned over is a Catch-22 for many boat owners.

For the fortunate few who can go out every week it won’t be an issue but the majority of boaties are going to have a problem with ethanol. Fuel stabilisers which keep ordinary fuel fresh won’t do a thing for ethanol.

There is only one additive that is claimed to cure the ethanol woes. It’s new to the market and we are about to start some testing. Watch this space.

The best advice from boat builders and oil companies has been to remove all ethanol-blended fuel from the system at the end of each trip unless you are certain that the boat will be used again within a week or two. That’s a basket of safety problems we don’t need to see.

We would like to see a serious advice and information scheme to educate the boating public. But please, not another government campaign – this is a case where the boating industry should run the show and the Government should foot the bill.

Special thanks to Ken Evans of Mercury and Paul Dawson of BRP-Evinrude for their advice.

– Gary Fooks


What the outboard manufacturers say:

• Modern outboards are fine with fresh ethanol up to E10 but manufacturers warn of fuel system risks.

• Evinrude says its motors can tolerate up to 10% alcohol in fuels, which is the maximum currently sold in Australia.

• Honda engines are designed for gasoline containing from 0% to 10% ethanol.

• Mercury engines will withstand up to 10% ethanol.

• Suzuki recommends pure gasoline without alcohol but up to 10% ethanol if necessary.

• Tohatsu recommends fuel up to 10% ethanol. Voids the warranty for all alcohol-fuel related malfunctions.

• Yamaha: All 2008 and later models are suitable for use with E10 fuel. Models prior to 2008 are not suitable.

Only in America

In June a California law firm filed a class action lawsuit in US District Court alleging oil companies failed to inform boat owners that ethanol causes damage to fibreglass fuel tanks.

The suit seeks to represent all owners of boats with fibreglass fuel tanks who filled their tanks with ethanol-blended gasoline from a California retailer. The suit also seeks to represent all persons in California who own boats with fibreglass fuel tanks that had to be replaced because of damage caused by ethanol-blended gasoline bought from a California retailer.

The lawsuit names major oil companies, including Chevron and Exxon Mobil Corp., as defendants.

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