Is E10 ethanol fuel suitable for marine engines?

By: Andrew Norton

9841_p.jpg 9841_p.jpg
Alcohol fuel tester The author's alcohol tester. Alcohol fuel tester

Our resident engine reckons unleaded E10 (ethanol) fuel is unsuitable for marine engines.

Is E10 ethanol fuel suitable for marine engines?
Putting E10 ethanol fuel into your outboard may not be such a good idea.

Over the past few months I have been getting reader enquiries about E10 unleaded petrol ethanol fuel for outboard motors (which contains 10 per cent ethanol). The readers have been asking, in view of diminishing availability of standard 91 RON ULP, is E10 ethanol fuel suitable for marine engines?

The answer is "NO" and according to marine fuels expert Ken Evans of Mercury Marine there are several reasons why this fuel should not be used, even though all current model outboards, be they two or four-stroke, will run on this fuel.



According to Ken, the primary reason is the extremely short shelf-life of E10, which is around two weeks from the time it leaves the refinery. The fuel literally goes "stale" after this period and has to be ditched, because of "phase separation". This is where any moisture in the petrol is absorbed by the ethanol, which then separates from the petrol itself. The water/ethanol mix is heavier than petrol and sinks to the bottom of the fuel tank, right where the fuel pickup is located.

This mix passes through the carburetor(s), or fuel injection system, resulting in expensive repairs. In the case of premix two-strokes, the water/ethanol mix contains no lubricating oil, so the engine will seize in a very short period.

Additives are currently available that claim to fix the phase separation problem, but Ken says once this has happened with ethanol fuels the only remedy is to ditch the fuel.

Another problem with E10 is the sometimes variable percentage of ethanol in the petrol. Ken says that the ethanol is added to the petrol after it leaves the refinery, and there is no guarantee of the percentage added. According to Dave Denny of Lakeside Marine, the national Tohatsu Outboards distributor, reports from ethanol percentage tests conducted in the US indicate that E10 may contain up to 48 per cent ethanol, which of course voids all new motor warranties should the powerhead fail from excessive ethanol in the fuel. Extensive alcohol-content surveys of fuel outlets undertaken in the US indicated that most of the fuels had a higher ethanol content than stated on the pump bowsers.



Ethanol can also attack underfloor fuel tanks in boats and the fuel-lines if they are not specially designed for this fuel. Ken says that fibreglass fuel tanks made before 1992 are particularly susceptible and in recent years there have been lawsuits in the US for the damage ethanol fuels have done to fibreglass tanks. The Haines Group, manufacturer of Signature Boats, warns owners not to use E10 in underfloor fuel tanks.

Because ethanol is a solvent, it slowly dissolves the resin in the fibreglass, which in its dissolved form, passes through the fuel filter and fuel-induction system into the engine. This coats the intake valves in four-strokes and damages the engine in a very short period.

The plastic remote fuel tanks supplied with all current-model portable engines are resistant to ethanol, but must not be used for storing the fuel, even if it’s non-ethanol unleaded.

Ethanol has only 65 per cent the calorific value (combustion efficiency) of non-ethanol petrol and using E10 will not only reduce engine performance, but also increase fuel consumption, despite its slightly higher RON rating of 92-93 compared to 91 for non-ethanol petrol.

Being an oxygenated fuel, ethanol will increase the air/fuel ratio of engines in direct proportion to the percentage of ethanol in the fuel.

For example, if E10 is used then the normal air/fuel ratio of 14.7:1 will be leaned out to 16.2:1. Not only does this reduce the engine efficiency by running too lean, but it can also damage four-strokes by raising combustion chamber temperatures and burning out exhaust valves.

Ken says that common problems with engines using E10 include stalling on acceleration (whether carbie or fuel-injection) and vapour-lock during hot re-starts.



When ethanol-extended petrol was first released in Australia in the mid-90s, problems started appearing with older engines using this fuel. In the US, Briggs and Stratton, manufacturer of four-stroke power equipment and industrial engines, had already experienced problems with alcohol fuels in its products, so it released an alcohol test kit through its Aussie dealer network in the late nineties.

I’ve used one for more than a decade now and it’s extremely accurate in measuring the percentage of alcohol in the petrol.

Basically, it comprises a glass tube with a screw-on plastic cap. The user simply needs to follow four simple steps to find out if there’s any alcohol in the petrol.

Water is added to the lower line, then petrol to the top line. After replacing the cap, the tube is shaken vigorously and stood upright for 10 minutes to allow the mix to settle. Should any alcohol be present the water level will rise above the lower line. The tester will then indicate if alcohol is present, up to a maximum of 30 percent alcohol. Tests I’ve recently conducted with standard unleaded from my local fuel outlets thankfully indicate no ethanol in the petrol.

Ken says that all Mariner, Mercury and MerCruiser dealers will be issued with an alcohol test kit, which will not only assist with engine problem diagnosis, but will also help dealers ascertain whether an owner can claim warranty in the event of powerhead failure. Dave said Lakeside Marine is also issuing Tohatsu dealers with alcohol test kits.


Boat engines

More boat engine reviews

Find marine engines for sale.



Want the latest stories delivered straight to your inbox? Sign up for the free TradeBoats e-newsletter.