Frequently Asked Questions

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  • Are Yamaha engines compatible with E10 fuel?

    All 2008 and later outboard models have been designed with fuel system components that are tolerant to fresh fuel containing ethanol up to 10% (E10). Outboard fuel systems can still be affected by: water, dissolved gum, varnish, corrosion particles, and dissolved resins that E10 fuel has cleaned from the distribution system and your boat’s fuel tanks.

  • What can I do to prevent issues with E10 fuel?

    Total prevention of issues may not be possible but there are steps you can take to minimize the occurrence and severity of the negative affects of E10 fuel:

    • If at all possible, do not use E10 fuel.
    • Ideally (before switching to E10 fuel) have your fuel tank completely drained to remove any accumulated water. As little as 500mls. of water can promote phase separation in 100L of E10 fuel. The result would be 10L of unusable ethanol and water mixture on the bottom of the tank.
    • If the tank can be completely drained, the internal surfaces should be mechanically cleaned to remove rust or aluminium oxides. Fuel polishing companies may be able to provide this specialized service.
    • Consider replacing the fuel tank in an older boat.
    • If your boat has fibreglass fuel tanks built prior to the early 1990’s, consult with your boat builder concerning E10 compatibility.
    • If unable to completely drain and clean your tank before switching to E10 fuel, add as much E10 fuel as possible to minimize the possibility of phase separation. Example: 500mls of water may cause phase separation in 100L of E10 but 500mls of water in 120L would be safe from phase separation.
    • Install a Yamaha 10-micron water separating/fuel filter between the boat’s fuel tank and the engine.
    • Change the 10-micron filter every 25 hours of use until there are no indications of excessive water and contaminates collecting in the filter. Normal filter changes are recommended every 50 hours of use.
    • Carry extra filters and change more frequently if there are indications the efficiency of the filter is rapidly diminishing due to excessive water and contaminates.
    • Buy brand name fuel.
    • Buy fuel from the same source if possible.
    • Buy fuel from stations that have newer, cleaner storage tanks.
    • Do not drain a used filter and reinstall. Contaminated fuel can enter the filtered side of the filter while draining.
  • Can I use fuel with a higher percentage of ethanol, such as E15 or E85?

    No, all of the negative issues discussed above will be increased and may cause major damage to the engine.

  • Why do boats seem to have more issues attributed to E10 fuel than cars

    Cars can have issues but are somewhat more tolerant due to typical usage patterns and differences in their fuel systems. Major differences are:

    • Modern automotive fuel systems (fuel filler, fuel tank, distribution lines and engine components) are closed or non-vented. Once the fuel is pumped into the tank, there is very little circulation of outside air (containing moisture) into the fuel system.
    • Boats are operated and often stored in a very wet environment increasing the risk of water directly entering the fuel system.
    • Boats have vented fuel systems which allow moisture laden air to circulate into the fuel tank as the fuel is drawn out of the tank and as the fuel expands and contracts during heating and cooling cycles of the outside air.
    • Automotive fuel tanks are typically much smaller than boat fuel tanks and are refilled more frequently. A full tank of fuel in a car or truck, typically 50-70 litres, may be used and refilled every week or two. Boat fuel tanks, typically 70-100 litres per tank, may only be refilled once a month during the boating season and typically may sit unused for many months during the off season.
    • Some boats use fibreglass fuel tanks. Polyester resins can be dissolved by ethanol.
  • How long can E10 fuel be stored?

    There are many different opinions concerning how long it is ok to store any fuel (E10 fuel or petrol), 2 weeks, 90 days, 1 year, or longer, before losing the properties that are required for proper and safe operation of your engine. There are too many variables (e.g., the age of fuel when purchased, temperature, humidity, use of stabilizers and the type of storage containers) to accurately predict how long.

  • Can I use the petrol remaining after removal of the phase separated water and alcohol?

    No, as mentioned above, the remaining petrol will have a lower octane level that may not be compatible with your engine.

  • Can phase separation be reversed?

    No, there are no additives or processes that will recombine phase separated ethanol and petrol.

  • What happens when phase separation occurs

    Several things happen:

    • The ethanol and water molecules settle to the bottom of the fuel tank forming a distinct layer of water & ethanol on the bottom and petrol without ethanol on the top.
    • Fuel for the engine is drawn from the bottom of the tank. An engine will not run properly, if at all, on ethanol and water. The ethanol and water mixture is very corrosive to some metals and can damage internal engine components.
    • The remaining petrol, without ethanol, will have an octane level below the original E10 fuel’s octane level, approximately 2 ~ 3 points lower. This octane level may be below the requirements of the engine.
  • What issues are caused by ethanol’s attraction to water?

    Ethanol molecules have a stronger bond to water molecules than to petrol molecules. In the absence of water, ethanol and petrol molecules will bond. When water is added to E10 fuel, the bond between the ethanol and petrol will weaken. When the percentage of water in E10 fuel reaches approximately 0.5%, the bond between the ethanol and petrol molecules will breakdown and the ethanol molecules will attach to the water molecules. This is called phase separation.

  • Wouldnt the cleaning properties of ethanol be good for a fuel system

    No, fuel systems that have been used for non-oxygenated fuel will have varnish deposits and surface corrosion (rust and aluminium oxides). This includes the tanks and pipes used for fuel storage and transportation. Ethanol will clean varnish as well as surface corrosion from any surface it contacts. Ethanol may dissolve plastic resins used to make some fibreglass tanks. The amount of material cleaned from all of these systems can quickly exceed the filtration capacity of fuel system filters resulting in restricted fuel flow. Ultimately engine performance is reduced and potentially damage to the engine can occur.

  • What are the negative properties of ethanol

    Ethanol has several properties that contribute to fuel system issues.

    • Ethanol is a strong cleaner (solvent).
    • Ethanol is hygroscopic (e.g., it has a strong attraction to moisture).
    • E10 fuel’s usable life span may be less than the normal length of off-season boat storage.
  • When is ethanol added to petrol?

    Ethanol is added to petrol by local or regional distributors.

  • What is ethanol?

    Ethanol is highly refined alcohol that is made from grain (typically corn) or the cellulose from other plants.

  • What is E10 fuel?

    E10 fuel is a blend of ethanol (10%) and Petrol (90%).