Since late 2021, all petrol stations in the UK supply E10 fuel as the standard grade available. This fuel contains 10% ethanol, an increase of 5% from the previous fuel; E5, which is still the standard for premium fuels.  

With over 39 million vehicles on the road in 2021, a change in the fuel they use, can be very impactful. The primary reason for the switch is the government's aim to reduce carbon emissions, we’ll explain how below. 

What is E10? 

E10 and E5 are classed as ‘Biofuels’, as 10% and 5% respectively of the volume is produced from crops. Ethanol is traditionally produced from the fermentation of sugarcane or corn, and has a similar, but not identical, energy content to petrol.  

It is estimated that the switch to E10 will reduce overall emissions equivalent to that of removing 350,000 cars from UK roads, equal to 750,000 tonnes of CO2.  

This is possible in part due to the CO2 absorbing qualities of the plants before harvesting, which offsets the CO2 released when they are burnt. 

Can I use E10 fuel safely? 

This is directly linked to the age of your vehicle, Ethanol has a higher solvent content than petrol, and as modern cars have been designed and manufactured using different materials, they typically fare better.  

One of the areas that E10 can have a negative impact is in your fuel systems’ seals and gaskets. These are often made of rubber on older vehicles, a material than Ethanol will degrade much faster than petrol. 

The UK government has published an online tool for checking if your vehicle is compatible, it uses your car's make to display information from the manufacturer on which cars are safe for use on E10. 

Whilst this tool is handy for most vehicles, it is always best to consult your owner's manual for more information. Almost all motorcycles are incompatible, due to the construction of their fuel and injection systems.  

A very simple rule to follow is if your car is pre 2003, err on the side of caution and read to the bottom of this article where we discuss alternatives. There are however a few car manufacturers that are not compatible even after 2003 so it’s always best to check manually. 

What if I’ve filled up with E10 in an incompatible car? 

It’s easily done, especially with the new fuel only being in use for a short period, the good news is that it’s not terminal.  

It’s best to not leave the E10 sitting in the tank and fuel system for too long though, if you drive the vehicle regularly, top up with E5 fuel at around half a tank, to dilute the E10, and continue as normal. 

If you’re intending to leave the car for a long period, or you do not drive much, it may be safer to drain the tank of E10. In this case it’s best to consult a specialist garage or dealer for advice.

What are other downsides to E10 fuel? 

As discussed, E10 fuel can cause issues with seals in older vehicles, but there are downsides to the new mixture, even for modern vehicles. 

Petrol has a higher energy density than ethanol, that means that E10 fuel has a lower energy density than E5. In older cars, this can mean reduced fuel efficiency, as there will be more fuel needed to travel the same distance.  

In modern cars however, the ECU and sensors can detect the changes in fuel properties, and adjust the engine timing and fuel injection accordingly. A Finnish study concluded in 2011 that using E10 results in the same miles per gallon as E5.  

Ethanol is also hygroscopic, meaning that it absorbs water. If left exposed to the outside atmosphere for too long, the fuel will absorb moisture from the air. This can cause serious issues with steel fuel tanks, lines and engine components.  

Are there any alternatives to E10? 

If your car is incompatible with E10, it’s best not to risk using it. The issue is that there are only two options available: 

Premium Fuel 

Premium fuels such as Shell V-Power still only contain 5% Ethanol, as they are developed to be a higher octane fuel. This means they can be safely used in older or incompatible vehicles without risk of damage.  

The issue comes in that premium fuel is typically 10-20p more per litre to buy. This means a typical tank of 70 litres will cost £10 more than normal fuel. Over a year of 8,000 miles this could cost anywhere from £150 to £250 more in fuel. 

Can I convert my car to use E10? 

As the main problems with using E10 are the fuel system components, it might be possible to swap these for more modern materials that are compatible.  

There are companies that specialise in this service and charge around £400 to convert fuel lines, filters and gaskets.  

There is however the issue of water retention, many modern cars use plastic fuel tanks that are not susceptible to rust, and are chemically engineered to resist degradation for the solvents in ethanol.  

Unfortunately to replace a petrol tank would cost significantly more than the fuel lines, which would probably not be cost-effective for an older vehicle. 

Reducing costs 

If E10 isn’t suitable for you, but your vehicle is not worth converting to modern fuel lines and tanks, unfortunately, you will have to use premium fuel. 

Luckily there are ways to reduce the cost of running a car, including servicing and maintenance. Bumper allows you to split the cost of a repair bill into monthly payments, at no extra cost. 

Complete your application and see dependable garages and dealerships in your area by entering your registration and postcode on our website. 

Author - Joseph Law

Joseph has been writing about cars for over seven years and writing for Bumper for over two, blending his passion for automobiles with a talent for storytelling.

Joseph has written about engineering and cars for Autozilla, Komaspec, and several engineering manufacturers. When he's not writing or tinkering with one of his five cars, Joseph dreams of owning an Alfa Romeo 33 Stradale.