Petrol In Boats

6 September 2021

Paul Owen, Weaver Water Ski Club

BWSW member Paul Owen of Weaver Water Ski Club has kindly shared this communication with us relating to use of petrol in boats which we are forwarding with his much appreciated permission . . .

You may have heard about E10 fuel introduction from the press. If you are fully informed on the change you have no need to read further, but if not I trust you may find this informative.

If you have not become aware of the differences with E10 fuel and have a boat that is 10 years old or older I would strongly advise that you read up on this because E10 petrol which contains up to 10% ethanol will begin appearing at forecourts from today (September 2021 onwards). Boats running on LPG only are not affected, and the E10 change is a further reason to consider LPG. If you have a dual fuel boat or petrol only alternative fuel known as E5 will remain available (in the form of today’s super unleaded or (97+ octane). If you are in doubt if your boat can use E10 just use this fuel as normal (but it will cost you more to fill up as 97+ octane is more expensive) petrol pumps will now be labelled as E5 or E10. There are some links below, and there is a wealth of information on the net available already. Just search for E10 fuel.

Some examples are provided in the links below:
Dangers Lurking in E10 Boat Fuel (
E10 petrol: Everything you need to know about the fuel change | Daily Mail Online

In summary what this E10 change means for boat owners is that while almost all modern engines will tolerate E10, storage of E10 fuel especially over winter if your boat is “winterised” is likely to be the biggest short term risk for a boat owner. There is a risk of long term potential damage to fuel systems, and most affected for different reasons are 2 strokes.

The main long term risk to marine engines is likely to be dissolved fuel system components being deposited inside the fuel system because of the key characteristics of ethanol such as:

  • Ethanol is a powerful solvent, and is hydroscopic (absorbs moisture naturally)
  • E10 fuel may affect components in your fuel system if they were made before 2011 and not designed to work with Ethanol
  • Ethanol doesn’t stay mixed with petrol and separates over time, especially when standing, and stored E10 petrol will have a much shorter shelf life as a result

If you put E10 fuel (Petrol which now contains 10% Ethanol) in an incompatible boat it should run as normal, so there is no need to be worried if you have already used it, its the long term effect or storage that’s becomes the main risk.

In particular it’s not a good idea to store fuel containing E10 over winter in your boat because over time there is a risk that seals, plastics and metals that were not intended to be used with Ethanol can gradually deteriorate as a result of bio Ethanol's corrosive properties.

This is simply because the fuel system on older products may never have been designed with any expectation of having to work with 10% ethanol. Of particular concern for boat owners would be that E10 is more corrosive and does not store as well.

To quote from the linked articles:
'Because ethanol is hygroscopic, it absorbs water from the atmosphere. And that water, in turn, finds its way into your stored fuel over time.
'This results in increased water forming in fuel tanks over time. 'As ethanol is also a solvent it can eat through rubber, plastic and fibreglass, so hoses and seals are likely to perish more quickly because of the higher concentration of ethanol in E10.' leading to damage of fuel lines and carburettors causing corrosion in brass, copper, lead, tin and zinc components.
Any engine in a road vehicle made since 2011 should already have been designed to run on E10 fuel. The same date might not apply to a boat engine and fuel system, although your boat builder can provide further information, the theme is that older engines/vehicles/Boats etc will need the most care.
Where E10 fuel should most definitely be avoided is in two strokes (especially in small engines, so if you use 2 strokes eg chainsaws, strimmers, or an older outboard) please take further advice relating to 2 strokes and E10.

You could use E10 fuel without an issue and all might be fine. But you could also be unaware that an issue is developing which may take several years to develop and result in difficult to resolve fuel issues.

I trust you found this informative and it will help you avoid future possible E10 issues.

On another topic I should also add that for those with a diesel vehicle, Diesel fuel (since 2019) now contains 7% Bio fuel and is labelled as B7.

B7 Diesel fuel is affected in a different way because there is a different risk. For example B7 Diesel can go waxy over time especially if it gets moisture in it and the first signs are normally blocked filters. B7 Diesel can also be affected by biological growth known in the industry as “Diesel bug”.

Alternative fuels are available but not for road use (for example red Diesel is available by special order in B0 “no bio added”) for non-highway products which are intended to be used infrequently such as generators.
Again B7 diesel should not give issues providing it’s not stored for long periods, and is protected against condensation. It will be worth reading on protecting B7 and FAME if you ever need to store Diesel fuel (or park a Diesel vehicle for long periods) because like E10 petrol B7 would also not store as well for long periods either.