Ethanol Fuel

Boat Engines - Dangers and Precautions Necessary With E10 Ethanol-Blend Gasoline.

Read Summary Only: Precautions Necessary To Protect Your Marine Engine from E10 Fuels.

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Many Boat Owners, in recent years, have unknowingly used petrol, blended with too high (unsafe) levels of ethanol alcohol. Running on petrol with over 10 % alcohol in a marine engine will cause performance problems, and can also cause permanent damage to your marine motor.

Understanding the dangers and effects of alcohol / petrol, in addition to following all the necessary marine fuel system precautions, is now necessary to avoid any problems with E10 gasoline.

There has been much controversy, misinformation and confusion since the recent (2006) increased distribution of ethanol gasoline in the United States, Australia and other Countries.

Recent marketing gimmicks overseas by some fuel additive product companies, have confused boaters even more. These ads falsely claim their new products can "fix" or repair ethanol water-contaminated fuel...Phase-separated fuel can not be fixed, and it must be discarded.

Even high level, reputable government authorities, have recently published information that conflicts with previous articles and bulletins written years ago on ethanol.

Marine manufacturer fuel recommendations (eg. owners manuals), which in the past, often warned against using alcohol fuels, now document that up to 10 % ethanol in petrol is acceptable.

As more people are using E10, the necessary precautions and dangers are becoming more apparent and better documented.

Boaters looking for instant answers and solutions will not find them- But, increased knowledge and following all the necessary precautions can spare you from most of the inconvenience and problems with alcohol petrol ie E10.

All reputable authorities agree, that running on ethanol alcohol above 10 % will cause motor damage and/or performance issues with petrol-powered engines, and it is always unsafe to run on contaminated fuel.

Prevention is your best weapon against ethanol petrol.

Ethanol Fuel Background

E10 Is a gasoline blended with up to 10 % ethanol alcohol and is now in widespread use in the U.S and many other Countries. Australia is also moving through Government Legislation to Ethanol blended ULP at maximum10% levels (E10).Ethanol, ethyl alcohol, is made from corn, sugarcane, wheat, switch grass and other grains.

Alcohol is an excellent cleaner, solvent, anti-freeze and most important; ethanol is hygroscopic, meaning it will absorb large amounts of water.

Australian Government regulations and laws for ethanol fuel use and labelling differ from state-to-state, and are now constantly changing.

The most serious boat engine problems overseas, resulting from ethanol E10 use, have mainly occurred due to illegal amounts of ethanol (over 10 %) being incorrectly added at the petrol Refineries before delivery to the fuel distribution outlets.

Since using over 10 % alcohol petrol is dangerous, it will invalidate all marine company engine warranties.

Many ethanol problems, reported by boaters appear to be due to their lack of knowledge/information on how to properly manage alcohol fuels.

Many boat engine breakdowns in recent times are directly related to the mismanagement of E10 petrol.

Your marine mechanic may not even suspect or test the fuel as a possible cause of breakdowns. Many marine engine repair businesses have flourished as a result of ethanol petrol engine damage.

Several older engines can not use any fuels that contain alcohol. e.g. Certain fibreglass tanks, mostly manufactured prior to 1992, will decompose from alcohol.

Fortunately newer outboard engines (past 5 years) have been designed to be more compatible with alcohol fuels.

Reasons Boat Engines Have More Problems with Ethanol Petrol

Boaters, often store fuel in tanks longer than recommended for E10 (30 days max, less in hot humid conditions).

Cars, unlike boats, usually replace fuel every week or two, which will successfully prevent the possibility of water-contamination/phase separation.

Boat engines live in a water environment - Alcohol fuel loves to absorb water.

Ethanol E10 gas can absorb large amounts of water into the fuel tank, Lead, when previously used in conventional gasoline as a stabiliser did not.

Plus, boat engines usually last longer than cars. Still owning and using a marine engine from the 1970's or 1980's is not uncommon. * These older engine parts and tanks were not usually designed or tested to withstand the damaging effects of alcohol petrol.

* Several older marine engines (made prior to 1992) have plastic and rubber parts, and fibreglass tanks that are NOT compatible with E10 alcohol fuel.

Dangers, Engine Problems and Damage From Ethanol Gasoline in Marine Engines

Ethanol's adverse effects to boat motors involves all types of performance issues and disintegration and deterioration, drying and clogging of engine parts.

Signs and symptoms of ethanol problems and damage include:

Stalling, prematurely worn engine parts, rusting, clogging of fuel filters and carburettor jets, release of gunk and sludge throughout the engine, frequent water-contamination/phase separation of fuel, and eventually engine breakdowns and even some deaths.

Ethanol can cause a motor to run lean on fuel, due to water, will not burn, which will take the place of fuel, as marine fuel tank pick-ups are mostly at the bottom of the fuel tank.

Vapor lock (fuel starvation) is common when using ethanol fuels.

Alcohol fuels are very prone to phase separation, when the weight of the ethanol and water will sink to the bottom of the fuel tank and get picked up by the motors fuel system. (Even small amounts of water can harm the fuel system).

The initial symptoms, (of using a higher than acceptable concentration of alcohol in fuel, is usually engine stalling when you demand acceleration (WOT).

You'll notice other performance issues, such as increased stalling, misfire, hesitation and difficulty maintaining boat speed during trolling.

The long term dangers of ethanol (and other alcohol-blended fuels) are many, including deterioration of parts (rubber, aluminium, fibreglass etc.), rusting, fuel system clogging, and other varied damage to engine parts and components. Older engines are more prone to ethanol alcohol damage.

The most reported and troublesome issue with marine engines and ethanol fuel has been regarding the decomposition of certain fibreglass fuel tanks. There really is no solution to this issue, other than to replace the tank (very costly, time-consuming project); Lining or sealing the tank, for added protection, is sometimes possible.

1. It is dangerous to use greater than 10 % ethanol in marine engines.

Some Petrol supplies are illegally much higher. Check petrol with an alcohol fuel test kit to make sure ethanol present is less than 10%.

USA Note - A recent post on a Long Island, NY message board states,

"Believe it or not, some of the fuel samples tested 48 % ethanol and most were above the 10 % 'maximum allowable by law'.".

All reputable brands of marine engines sold in the Australia & NZ are designed to operate on fuel containing no more than 10 percent ethanol. Engines built before ethanol became popular for environmental reasons, (past 10 years) have minimal safeguards from the damage alcohol fuels will cause.

2. Ethanol absorbs water - Water molecules combine with petroleum (petrol) in your fuel tank and lines...

Ethanol has an increased risk of fuel water-contamination due to ability to absorb H20.

(Ethanol attracts and absorbs moisture from the air). Vapor lock and fuel starvation can occur.

The gasoline you pump in your tank may be dry, but due to condensation (from humidity, temperature, etc.) water does exist in your tank. Since water is insoluble in gasoline, it sinks to the bottom of your tank -

As long as it remains below the level of your fuel pickup tube it will not affect your engine however most marine tanks pick up from near the bottom of the tank. The problem is water is soluble in ethanol and will travel thru your engine fuel system.

A water/ethanol mixture, being heavier than Petrol, will sink to the bottom of the fuel tank, leaving a lower octane petrol on top. This low octane petrol (lean fuel) can cause performance issues with 4-stroke engines, and can cause damage to 2-stroke engines.

Excess water in engines will also cause premature rusting and corrosion of metal parts.

3. Ethanol is an amazing solvent and cleansing agent.

High levels of ethanol can dissolve, deteriorate and breakdown solid material, including rubber, plastic, fibreglass and even aluminium and steel.

Ethanol will also cleanse and release corrosive matter (gunk), varnish and rust, which will travel through the engine and clog fuel filters, carburettor jets and injectors. In many outboard engines it will also contaminate the fuel present in your fuel tank.

Ethanol tends to dissolve certain resins, which can travel through the engine intake and coat intake valves, causing sticking and bent pushrods or worse. This has been well documented in USA for boats equipped with certain fibreglass gas tanks, made before the early 1990's.

The more gunk (rust, sediment, dirt, etc.) collected in your outboard engine over the years, the more noticeable the cleansing effects of alcohol will be noticed.

Ethanol's solvent and cleansing abilities can lead to engine failure and expensive (avoidable) repairs.

4. Ethanol can wear-down and dry-out the plastic and rubber parts in your engine.

Rubber seals and plastic material used in older boats are often not compatible with alcohol. Ethanol will make engine parts dry and brittle. Since ethanol is a cleansing and drying solution, it will clean the oil right off the internal components of a 2 stroke, therefore extra lubrication maybe necessary. Good Marine Fuel stabilizers will help with this problem.

5. Ethanol blends can cause additional contamination by reacting chemically with MTBE fuel blends.

Do not mix petrol that contains MTBE with ethanol E10.

Mixing MTBE fuel with ethanol blend fuel can create a gel-like substance that clogs passages in carburettors.

Stalled engines and engine damage are the result. Fuel injected engines have

shown less damage, than carburetted engines, from this gel-like substance.

6. Engines with older fibreglass petrol tanks have the greatest risks when using fuel with ethanol.

Fibreglass petrol tanks can "deteriorate" from ethanol, causing this degraded resin stuff, (you'll see "black sludge") to circulate through your engine, coating intake manifolds and building up on intake valves - which basically destroys your engine.

1. If possible, try to avoid using ethanol fuel blends in your outboard and marine engines.

If you are unable to obtain alcohol-free fuel in your area, you SHOULD TEST THE FUEL YOU BUY to assure the ethanol content is at or below 10 %.

2. Follow engine manufacturer Fuel recommendations. Check with your marine motor manufacturer and/or check your owner's manual.


3. Always use fresh, high-quality gasoline and replace it every 2-4 weeks.

Always avoid storing Petrol in tank for greater than 30 days. Remember that Petrol with ethanol has a shorter shelf life - use it up and replace it quickly.

Buy Petrol from busy Service stations - Fuel turnover is faster, Petrol will be fresher.

4. Check your fuel tank for the presence of water and remove all water before adding an ethanol blend.

5. Avoid running on bottom of fuel tank (where most water will sink).

6. Do not mix MTBE and ethanol-blended fuels.

Run out or remove your old (MTBE) fuel before putting the new ethanol fuel in your tank.

7. Make sure your motor is equipped with a water separating fuel filter.

Mercury's Optimax, EFI and Four strokes (25hp & up),engine models have them, other engine brands may or may not. The installation of a water separator in the fuel line will help with small amounts of water. Mercury Marine's above engines are also equipped with water sensors.

8. Check fuel system for contaminants and clogging and replace your fuel filter often.

Fuel filters should be replaced at least every 50 -100 hours.

9. Quicksilver Fuel Stabaliser will stabilise fuel, inhibit corrosion and absorb moisture (water) without adding alcohol to the fuel. Add fuel stabaliser at every petrol fill-up in your boat.

10 . Mercury Marine recommends Quicksilver Quickleen be added to the fuel tank each time you add gasoline, (Reduces possibility of rusting, piston ring sticking and carbon build-up, better overall engine performance, increases engine life), but it will not remove water.

11. Keep your engine well-tuned and lubricated.

12. If your engine has an older fibreglass fuel tank, replace it. (Check with manufacturer if your tank was designed to tolerate alcohol fuels). Many newer fibreglass tanks are double-lined and made of special material that holds up to ethanol blended fuels.


Ken Evans – (putting the pieces together)

Marine Consultant – Government, Sales Training, Marine Business

Australia - New Zealand - Pacific

60 Riverview Rd, Pleasure Point
NSW 2172

Direct Phone +61 2 9774 2953
Office Phone +61 2 9774 2953
Mobile +61 408 413 456
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