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E10 Unleaded

Here we will look at what E10 unleaded is, Unleaded fuel history, the issues and problems it could produce especially within the internals of your classic vehicle, why protection grade E5 super or premium unleaded is recommended for classic vehicles and why more and more modern vehicle owners are switching to E5 ‘Super’ unleaded.

Not since the leaded fuel ban in 2000 has there been such a change to the UK fuel options, with similar reasons, the former Lead pollution which still makes up 40% of London’s airborne lead particles today, the Later CO2 carbon emission reduction.

When launched the government guidelines for the use of E10 fuel was that classics and some vehicle models made up to the early 2000s as well as vehicles 50cc or under should not use E10, it is also not recommended for two stroke motors.  From 2011 vehicles had to be made E10 compliant.

What is E10 Fuel?  E10 breaks down simply to Ethanol 10%, meaning that regular unleaded petrol will be 90% oil-based petroleum and 10% renewable ethanol, ethanol in its simplest form is pure alcohol.

Ethanol was first introduced to unleaded fuel in the UK in 2008 at E5 5%, while this made little difference in comparison to the traditional unleaded.  The Federation of British Historic Vehicle Clubs did have owners of motorbikes with fibreglass fuel tanks reporting damage and leaks.

With the introduction of E10 petrol, the government announced that 97plus octane fuel ‘Super’ would remain E5 and Historic, classics vehicles should use this, but why?

Ethanol is corrosive, while 10% may not seem like much, the higher content is believed to be able dislodge deposits within older fuel tanks etc.  Ethanol can eat brass, copper, lead, tin and zinc as well as corrode plastic and rubber fuel lines.  Ethanol is also hygroscopic, meaning that is absorbs water so can cause problems if left standing for long periods of time.  Experts also warn of issues with turbo assisted engines.

With damage from minor sticking carburettor floats, with soldered floats possibly fall off to Fuel lines perishing causing leaks and possible fire damage if undetected, there are several issues that can come up.  You can buy the correct fuel lines and parts to help counteract this.  Be careful if you do as there are a lot of cheap knock offs out there.  But is it worth it?

Ethanol is less energy dense than petrol so E10 fuel tends to produce a leaner fuel to air mix by up to 2.6% this also means that engines can run hotter if not correctly adjusted.

Being less energy dense also means that E10 doesn’t produce as many miles to the gallon as the fuel it replaces.  The government’s own impact assessment which calculated the energy loss of E10 to be 1.7% loss, estimating an extra £18 per month (Environmental Protection Agency EPA estimates a 3-4% loss).


So, if you are not so concerned about the CO2 emissions how does E10 fuel compare to super unleaded? 

E10 Unleaded

Currently priced at 139.9p per litre times that by 4.5461(litres to the gallon) gives you £6.36 per gallon, for this exercise we will say the average is 40mpg divide your gallon cost by that gives you 15.9p per mile on a £20 fill that would get you 125.8 miles.

E5 Super Unleaded (protection Grade)

Currently priced at 148.9p per litre times that by 4.5461(litres to the gallon) gives you £6.76 per gallon, for this exercise we will say the average is 40.8mpg 2%* more than regular unleaded, divide your gallon cost by that gives you 16.6p per mile on a £20 fill that would get you 120.5 miles.


Prices based on Costco fuel at time of writing.

On this calculation as you can see of a £20 purchase there is only a 5 mile difference between the fuels.

*Government estimate; 1.7% EPA; 2-4% so if you upped the 2% to 4% E5 ‘super’ produces 123.5 miles to £20 of fuel.


Personally, my daily drive uses E5 ‘super’, you can feel a difference in performance be that psychological or not. There is a 30–40-mile difference in the total mileage of a tank, granted a tank of ‘super’ may cost a little more but you are visiting the fuel stations less and looking after your internals.

It is also reported that more and more UK drivers are doing the same and filling up with ‘Super’.


If your interested in more detail on the effects of ethanol Matthew Tomkins, an associate of FBHVC and projects manager for Practical Classics magazine submitted his undergraduate thesis on this subject and has kindly given FBHVC permission to reproduce it here.

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