E10 fuel and classic cars: what the new petrol means for owners, the risks it and how to avoid damage

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How the new standard for unleaded petrol will affect older vehicles

In just a few days, the UK’s standard unleaded petrol will change with the introduction of E10 fuel.

From September 1, filling stations around the country will be required to sell the new formulation of fuel, with serious implications for drivers of older cars.

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E10 contains a higher bio-ethanol mix than the outgoing E5 petrol and is being introduced as part of efforts to reduce the CO2 emissions generated by transport.

Most modern cars can safely run on E10 petrol but the situation is not as straightforward when it comes to classic cars and even some relatively new models.

Is E10 petrol safe for classic cars?

All cars built after 2010 are designed to run on E10 and most cars built since 2000 are also compatible but owners of cars older than that could run into problems if they use E10 for prolonged periods.

According to the Department for Transport (DfT) study into the introduction of E10, around 700,000 cars in the UK’s are “not warranted by their manufacturers to use E10”.

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The RAC estimates that as many as 350,000 of these may be middle-aged vehicles in daily use, with the rest representing the UK’s varied classic car scene.

The DfT says that the number of incompatible vehicles is expected to decline as vehicles “come to the end of their life” but acknowledges that some classic and cherished cars which are not E10-compatible will remain in use.

What are the risks of E10 petrol to classic cars?

The main threat to classic cars from E10 petrol is the higher level of ethanol in the fuel. E5 petrol contains up to five per cent bioethanol while E10 contains up to 10 per cent.

The first problem is that ethanol is a solvent and can damage rubber, plastic and fibreglass components, such as fuel lines, filters and fibreglass petrol tanks. Ethanol can cause cracking and splitting of such components. At best, this means they need to be replaced more frequently and, at worst, it creates a risk of fuel leaks and fire.

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Ethanol is also hygroscopic, which means it absorbs water from the atmosphere. Classic car experts warn that this could lead to condensation forming, especially if a car is left unused for prolonged periods. This in turn could lead to corrosion in key metal areas such as the fuel tank and carburettor.

Hundreds of thousands of classic cars are affectedHundreds of thousands of classic cars are affected
Hundreds of thousands of classic cars are affected | Shutterstock

There have also been warnings that due to the different composition of the fuel it can cause lean running in older engines, and the higher ethanol content could loosen desposits in the fuel system, clogging filters.

What can owners do?

Although E10 is becoming the standard fuel, E5 will still be available at many forecourts, at least in the short term.

Petrol stations which offer two grades of fuel will continue to sell E5 but only as the higher-grade super or premium 98 RON unleaded, which is around 11p per litre more expensive.

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In some rural areas, such as north-west Scotland, where filling stations have only one pump, E5 will also remain on sale.

The DfT has said that E5 will remain on sale for at least the next five years.

Owners of classic cars can also modify their cars to run safely on E10 fuel, using compatible materials for elements such as fuel lines. However, the cost of such work is estimated to run into hundreds of pounds for some vehicles.

An accidental or enforced top-up with E10 is unlikely to cause lasting damage but owners of classic cars are being advised to avoid regularly using E10 unless their car has been modified to ensure all components are E10-compatible.

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