Will E10 Petrol Affect My WaterMota Boat Engine?

Published: 29 Jul 2021



E10 Petrol LogoE10 petrol is coming to the UK in September 2021 and as with the introduction of unleaded, and more recently E5 petrol, there is a concern as to how this may affect the running of marine petrol engines and more specifically WaterMota engines, especially those in Freeman’s.

Below are our thoughts based on the information we have gathered, please do not take the information below as final or even correct. It is a new scenario for all of us but the introduction of unleaded and E5 passed without incident, and we expect this to as well.

What is E10 Petrol?

E10 Petrol contains up to 10% renewable ethanol which is designed to help reduce carbon dioxide emissions. By blending petrol with renewable ethanol less fossil fuel is used in the production of petrol and therefore creating less CO2 emissions when it is burnt. E10 is starting to appear on UK forecourts and will be clearly marked on the petrol pump. Super Unleaded will remain as E5 for at least a few years but may not be available at all petrol stations.

The Problem with E10 Petrol in Boats

Ethanol blended fuels can start 'phasing' or phase separating, this is when the ethanol in the fuel absorbs too much water, separates from the petrol, and drops to the bottom of the tank as the ethanol and water combination is then heavier than the petrol.

Phase Separated Petrol from a boat

Will E10 Damage My WaterMota Boat Petrol Engine?

In short E10 petrol isn't likely to cause any more harm to your engine than E5 petrol or even from the original change from leaded to unleaded petrol. The real problems will come from the storage of E10 petrol in your boat, and the resulting water build-up while you are not using it, such as over winter.

Once E10 (or even E5) petrol has completely separated (phase separation) no additive can reverse the change and the fuel tank and fuel system will require draining and thoroughly cleaning. Any remaining fuel from your tank will be unusable.

E10 Phase Separation & Water in The Fuel Tank

The easiest defence against phase separation is to keep the tank nearly full, but not completely full.  Keep the level a gallon or so from full to allow for fuel expansion, never retain fuel in the filler hose as this may increase the pressure on the fuel system and encourage fuel seepage.

If you overfill the tank up into the fuel filler hose, always check the tank joints, fuel line and carburettor for seepage before starting and then use up the amount of fuel stored in the hose, plus a bit more to allow for fuel expansion.

Moisture in the petrol forms primarily due to the empty space in the tank, therefore reducing the amount of air in your petrol tank will reduce the amount of water that can enter with the air, and in turn be absorbed by the ethanol. This is especially important when the boat is being left for any period of time such as during the winter layup.

E10 Petrol Corrosion & Debris

Ethanol may contribute to corrosion in the fuel components, it can also loosen debris that normally collects in the corners of the fuel tanks which can lead to clogged filters, fuel lines or even carburettor jets.

Phase Separated Petrol from a boat

How to Combat the Problems With E10 Petrol in a Boat

The good news is that E10 petrol has been used in many parts of the world for over 25 years so there are proven ways to protect your engine from the potential hazards of E10 Petrol.

  • Use a fuel stabiliser such as Fuel Set or Star Brite Star Tron to help combat water in the fuel and to help slow down the oxidization of petrol. This is especially important when you are leaving or storing the boat for a period of time without use.
  • Ensure you have a fuel filter, and renew fuel filter elements regularly.
  • Ensure you inspect and clean fuel lines regularly.
  • Regularly drain and clean the water trap if fitted.
  • Use Super Unleaded (E5) Petrol where it is available.
  • Buy Petrol from reputable petrol stations, preferably ones with a high turnover of petrol.
  • Do not store 'extra' petrol in cans for long periods as petrol oxidises as soon as it is exposed to air. Keep Petrol clean and fresh.
  • Use your boat more! The more you use your boat the fewer problems you are likely to have with bad fuel.

Using a Petrol Additive in a Boat

Starbrite Star Tron Petrol TreatmentFuel Set Fuel Conditioner For PetrolIt is probably a good idea to start using a petrol additive such as Fuel Set or Star Brite Star Tron if you are not already. The fuel additives help reduce the amount of water that can build up in your petrol tank as well as helping to condition the petrol and keep it clean. Generally, fuel additives should be used every time you fill up with new petrol.

Fuel Filters, Water Traps & Boat Fuel Systems

It is more important than ever to make sure you have a fuel filter fitted in your fuel line; some early installations still haven't had one fitted. It may also be wise to fit a water trap in your fuel system to specifically collect any water that has made it from the tank before it gets to the fuel filter.

E10 Petrol & Boat Engines - Enjoy Boating!

There was a concern when unleaded petrol first came in and later with E5. Both events passed off without major concerns and it is likely that the E10 situation will too. There is still Super unleaded available for a few years yet, using that will give time to sort any unforeseen issues out.

We are lucky that our engines are relatively cold running and at a more or less constant speed, they are not high-performance engines as this apparently helps alleviate the effects too.

Most of all do not worry too much! Use fresh petrol, use a fuel additive, replace your filters, and inspect your fuel lines regularly, but most of all enjoy boating!


Commonly Used Fuel Filters To Help With E10

The following filters may be commonly found on petrol boat installations. It is a good idea to fit a fuel filter and ideally a water separator as well.

Petrol Conditioners & Cleaners

Useful products for looking after your E10 Petrol and cleaning your fuel tank if required.

Fuel Set Fuel Conditioner Concentrate
from £12.95
Save: £3.14 (20%)
Star Tron Fuel Additive
from £16.36
Save: £4.86 (23%)
Star brite Star Tron Fuel Tank Cleaner
£43.35
Save: £18.62 (30%)
Star brite Ez-to-Store Ez-to-Start Fuel Additives
from £15.36
Save: £3.65 (19%)