Text Box:    The fuel requirements from a 2008   Evinrude E-TEC operators guide  E10, or unleaded petrol (ULP) with 10% ethanol, has been around for more than 20 years but only recently has it gained widespread publicity in Australia.  Back in the 1980’s, many large cities in the USA mandated what was often called “reformulated gasoline” (RFG). It was unleaded petrol with either 10% ethanol or up to 15% MTBE – both of which contain some oxygen in the liquid to help to improve combustion, thereby lowering tailpipe emissions on cars.  They were tackling a local air pollution problem.

Today we’re becoming familiar with E10 because it lowers our dependence on imported oil and helps reduce our global emissions.  MTBE was later found to contaminate ground water with a nasty taste, so has now been removed from commonly available fuels, leaving ethanol as the only current easy solution as a substitute for petrol.

Since the mid-1980’s all Evinrude and Johnson outboards (and all other major brands of outboard motor) have been designed to run safely on RFG or E10. That required changes to fuel line materials, rubber or elastomer parts, and some fuel system metal components. Owner’s guides since those days will mention that fuel with up to 10% ethanol (or 5% methanol plus co-solvents) are OK for use, without any changes needed to the engine.

The Plus Side

Ethanol has some very good features –

  • Higher octane, so detonation is reduced in highly stressed engines.
  • It’s produced from a renewable resource (crops) so it’s not a finite resource and it reduces our use of imported oils.
  • It is cleaner burning than petrol, so reduces emissions.
  • It is an Oxygenate, so more complete combustion is possible, lowering overall emissions.
  • Already safely in use all around the world so most recent engines and fuel systems are fully compatible.

The Minus Side

Ethanol has some characteristics that are different to petrol –

  • It is a better solvent, so dirt and gum deposits in your fuel system that petrol did not move can be flushed out with ethanol, creating blocked filters in older systems. It will also attack the resins in some fibre glass fuel tanks.
  • When added to petrol the fuel becomes more electrically conductive, so corrosion of metal fuel system components can be a problem.
  • It has higher volatility (changes from a liquid to a gas more easily) which can create vapour lock and driveability problems.
  • It is Hygroscopic (absorbs moisture from the air) which can lead to storage problems, when the water combines with the ethanol and separates out from the petrol. This called “phase separation” as the resulting fuel then has distinct layers, ethanol/water on the bottom, and petrol on the top.

Adapting to E10, Avoiding the Pitfalls

If you have an Evinrude or Johnson outboard made since 1986 (and most other major brands) the engine is already fully compatible with E10; however the fuel system inside your boat may need careful monitoring.  If you have a fibre glass fuel tank and you not sure if the resins used were alcohol resistant, then it would be best avoid using it or get it checked out, before you get a leak problem.

Fuel filters may become clogged shortly after first switching to E10 in older systems, so carrying a spare filter element, and knowing how to change it, is essential.  If you’re not entirely sure that all of your fuel system components (hoses, clamps, fittings, filter, primer bulb etc.) are ethanol resistant, then you should get it checked out and closely inspect your entire system before each outing.

Text Box:    How do you know you are buying E10? By law, all petrol bowsers must display a sign similar to this, showing the maximum Ethanol percentage.  Some older carburettor engines may experience vapour lock problems. These show up as hard starting on a hot day, stalling or slow to accelerate after idling for a while.  Some engines may require carburettor adjustments or jet changes to run properly on E10.  Today’s fuel injection engines, with their pressurised fuel systems, rarely experience any vapour lock problems

The most likely problem most of us will encounter is phase separation in storage.  Because boat fuel tanks are usually unsealed and have open breather lines, air can freely flow in an out of the fuel tank with daily temperature changes. When the temperature drops each night, moisture in the warm air inside the fuel tank condenses on the walls, then runs down to the bottom of the tank. If the water content reaches about 0.5% of the ethanol content, and it’s a nice warm day, then you can get phase separation. Then, the fuel at the bottom of your tank, where the engine’s fuel is drawn from, becomes just ethanol and water.  Engines designed for petrol will not run properly, if at all, on straight ethanol.

Recreational boat use averages about 50 hours per year. That means for every hour you spend on the water your boat will spend about 200 hours, sitting on the trailer or in the berth.  Cars are unlikely to suffer phase separation because they are used nearly every day and the fuel is rarely more than a couple of weeks old.  Phase separation is also rare in underground storage tanks because they are kept at a more constant, cool temperature and the fuel is generally used within a few weeks.

The Best Storage Tips for Boats Are –

Not using the boat for just few a few weeks -

  • Fill the tank with straight ULP or PULP (without ethanol).
  • If you must use E10, fill the tank while adding a fuel conditioner to your fuel, then run the engine to get the treated fuel throughout the system.

Not using the boat for several months or until next season –

  • Fill the tank with straight ULP or PULP (without ethanol) while adding a fuel conditioner to your fuel, then run the engine to get the treated fuel throughout the system
  • While it depends on temperature and humidity you probably can’t avoid phase separation and oxidation of E10 fuel over this time period, so it is then best to completely drain the system and leave it empty.

Is More Better?

If 10% ethanol helps, then what about using 20%, or more? 

  • As the Ethanol content increases so does its ability to attack fuel system components.  Engines designed for higher ethanol content fuels (E85 for example) have many different fuel system components to engines designed for ULP or E10. Using higher concentrations without the system being designed for it, can lead to dangerous fuel leaks and fires.
  • The energy content of ethanol is considerably lower than petrol, so the engine “calibration” (amount of air mixed with the atomised fuel) needs to be changed for the engine to run properly.  The chemically correct air to fuel ratio for Petrol is 14.7 to 1 (by weight).  For E10 fuel it is 14.0 to 1, not very far away from ULP and within the range modern engines can handle with out modifications.  (For comparison E85 requires a ratio of 9.7 to 1)
  • More than 10% ethanol requires changes to nearly all engines, so unless the engine is designed for it, more than 10% will most likely cause problems.
  • While E10 makes almost no difference to fuel economy, that is not the case if the ethanol percentage increases. For example E85, which is currently used in many countries around the world in specially adapted cars, requires 30 to 40% more fuel volume for the same work output. That means your fuel range drops by 30+%. Not a big problem with most cars, but an important consideration for boats where refuelling facilities are often few and far between.

Paul Dawson
Service Training Manager
BRP Australia Pty Ltd