Recent news

Problems with current (E5-E10) Unleaded Petrol

We are seeing an increasing number of breakdowns and running issues caused by the new generation of ‘environmentally friendly’ modern fuels (E5 & E10).


The average boat owner is unaware there are any issues with theses fuels until it’s too late and we see them in the workshop.


Please take a moment to read the below artical about the issue.


Ethanol Fuel Background:


E5 / E10, Is a blended unleaded petrol with up to 10 % ethanol alcohol & is now in widespread use in Europe. Ethanol, ethyl alcohol, is made from corn, sugar & other grains. By law petrol retails must inform their customers if the unleaded fuel they are selling is blended with Ethanol Alcohol by a ratio of 10% or more (E10), fuel sold to this new specification must be clearly labelled on the pump as ‘unleaded petrol 95 E10’


Alcohol is an excellent cleaner, solvent & anti-freeze, most important, ethanol is hydroscopic, meaning it will absorb large amounts of water, this will, in time & left unchecked have adverse effects to both inboard & outboard motor fuel systems & will lead to performance issues, disintegration, deterioration, drying & clogging of engine fuel system parts.


Signs & symptoms of ethanol problems & damage include:


Stalling, prematurely worn engine parts, internal rusting, clogging of fuel filters & carburettor jets, release of gunk & sludge throughout the engine, frequent water contamination /phase separation of fuel, & engine fuel related breakdowns.


Ethanol can cause a motor to run lean on fuel, due to water that will not burn, which will take the place of fuel.

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


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


If this happens you'll notice performance issues, such as increased stalling, misfire, hesitation & difficulty maintaining boat speed during trolling.


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


The most reported & troublesome issue with marine engines & ethanol fuel has been regarding the decomposition of certain fibreglass petrol 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.


Why should Boaters worry about this new fuel & why should they treat it’s use differently ?


Boaters often store petrol in tanks longer than recommended, for E5 / E10 (60 days).

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


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

Ethanol E5 / E10 petrol can absorb large amounts of water into the fuel tank, conventional petrol did not, plus, boat engines usually last longer than cars. Still owning & using a marine engine from the 1970's or 1980's is not uncommon. * These older engine parts & tanks were not usually designed or tested to withstand  the damaging effects of alcohol (E5 / E10) fuels.


* Several older marine engines (made prior to 1992) have plastic & rubber parts, & fibreglass tanks that are NOT compatible with E5 / E10 alcohol fuel.


Main Issues to Keep In Mind


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

 (Ethanol attracts & absorbs moisture from the air). Vapour lock & fuel starvation can occur.


The petrol you pump in to your tank may be free from water, but due to condensation (from humidity, temperature, etc.) water does exist in your tank. Since water is insoluble in petrol, 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 & will travel thru your engine fuel system.

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



2. Ethanol is an amazing solvent & cleansing agent - High levels of ethanol can dissolve, deteriorate & breakdown solid material, including rubber, plastic, fibreglass & even aluminium & steel.


Ethanol will also cleanse & release corrosive matter (gunk), varnish & rust, which will travel through the engine & clog fuel filters, carburettor jets & 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 & coat intake valves, causing sticking & bent pushrods or worse. This has been well documented for boats equipped with certain fibreglass petrol 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 & cleansing abilities can lead to engine failure & expensive (avoidable) repairs.


3. Ethanol can wear-down & dry-out the plastic & rubber parts in your engine - Rubber seals & plastic material used in older boats are often not compatible with alcohol. Ethanol will make engine parts dry & brittle. Since ethanol is a cleansing & 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 petrol’s that contains MTBE with ethanol E5 / E10.

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

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

How to Prevent Damage from E5 / E10 Fuels


1.  Always use fresh, high-quality petrol & replace it every 2-4 weeks.

Always avoid storing petrol in tank for greater than 90 days. Remember that petrol with ethanol has a             shorter shelf life - use it up & replace it quickly.


2. Buy petrol from busy petrol stations - Fuel turnover is faster, petrol will be fresher.


4. Check your petrol tank for the presence of water & remove all water before adding an additional fuel


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


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

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


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

The installation of a water separator in the fuel line will help with small amounts of water.  Some marine           engines are also equipped with water sensors.


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

Fuel filters should be replaced at least every 50 -100 hours or at least once a year


9. If your engine has an older fibreglass petrol tank, replace it. (Check with manufacturer if your tank was         designed to tolerate alcohol fuels).  Newer fibreglass tanks are double-lined & made of special material that     holds up to ethanol.


10. All ways run your engine out of fuel, disconnect your fuel line or shut off your fuel tap & let the engine ‘run dry’ this will empty the system of most of the fuel.






© 2014 BHG Service

BHG Service Ltd, Bucklers Hard, Beaulieu, Brockenhurst, Hampshire, SO42 7XB, UK


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