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 carburetor jets, release of gunk and sludge throughout the engine, frequent water-contamination/phase separation of fuel, and eventually engine breakdowns and death.
Ethanol can cause a motor to run lean on fuel, due to water will not burn, which will take the place of fuel.
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, aluminum, fiberglass 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 fiberglass gas 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 gas supplies are illegally much higher. Check gas with an alcohol fuel test kit to make sure ethanol present is less than 10%.
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 marine engines sold in the United States 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 (gas) in your gas 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. The problem is water is soluble in ethanol and will travel thru your engine fuel system.
A water/ethanol mixture, being heavier than gas, will sink to the bottom of the gas tank, leaving a lower octane gas on top. This low octane gas (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.
3. Ethanol is an amazing solvent and cleansing agent.
High levels of ethanol can dissolve, deteriorate and breakdown solid material, including rubber, plastic, fiberglass and even aluminum and steel.
Ethanol will also cleanse and release corrosive matter (gunk), varnish and rust, which will travel through the engine and clog fuel filters, carburetor 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 for boats equipped with certain fiberglass 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, Extra lubrication is necessary.
5. Ethanol blends can cause additional contamination by reacting chemically with MTBE fuel blends.
Do not mix gas that contains MTBE with ethanol E10.
Mixing MTBE fuel with ethanol blend fuel can create a gel-like substance that clogs passages in carburetors.
Stalled engines and engine damage are the result. Fuel injected engines have shown less damage, than carbureted engines, from this gel-like substance.
6. Engines with older fiberglass gas tanks have the greatest risks when using fuel with ethanol.
Fiberglass gas 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.