E10 fuel is now the default petrol at the pumps. Here’s everything you need to know about this higher-ethanol fuel

Arriving in 2021 in a flurry of news, controversy and debate, E10 fuel has become the standard form of petrol available on UK forecourts. The previous standard, E5, has now been superseded and is only available in the form of more expensive premium-grade fuels.

As its name suggests, E10 petrol contains up to 10 per cent ethanol, twice the proportion of the E5 grade which has been the standard for the last decade. The issue of ethanol in fuel has long been a hot potato in the classic car world but at the lower concentration of the E5, fuel has proved not to be a problem in practice. However, the E10 grade has people worried about its effects on older cars.

There are two big issues with ethanol fuels and older cars. The first is that ethanol can have a corrosive effect on metal, plastic and rubber parts in the fuel system. The results of this can range from inconvenient, like sticking carburettor floats, to dangerous, such as when fuel lines perish.

Crucially, not all vehicles will have problems and rather like the introduction of unleaded fuel back in the ’80s, some will be perfectly happy on the new fuel and some will need modification.

The second issue with the E10 fuel and something which is more of a problem for classic cars than everyday modern vehicles is that the ethanol is hygroscopic, meaning it tends to absorb water. Clearly the longer a car is left standing idle, the bigger an issue this will be, with any moisture in the fuel only adding to potential issues.

Meanwhile, there are suggestions that some two-stroke engines – from motorcycles to old Saabs and chainsaws – are also ill-suited to the higher ethanol content found in the new fuel.

Why E10 petrol?

In theory the use of E10 petrol is an environmental move, intended to reduce the fossil fuel component of vehicle fuels and therefore combat climate change.

Rather than emissions or air quality, the goal is reduced CO2 emissions and it’s thought that by doubling the proportion of the renewable component in the fuel (the ethanol) a 750,000-tonne reduction in CO2 is achieved – the equivalent of taking 350,00 cars off the road.

It’s not all good though. The fuel is slightly less energy dense, meaning an economy reduction of up to 1%, but what’s not widely known is that since 2016 new cars have been certified for emissions and performance using E10 fuel.

What can classic owners do about E10?

Owners of modern classics can use the government’s online checker tool which uses information supplied by car makers as to the suitability of the fuel system. Information is patchy but has improved since the online check was first offered and for many brands the system will go as far back as the early 90s.

Some marques, especially the German brands, go back even further: Volkswagen for example simply states that all its engines can run on E10 fuel except for a few FSI units from the early 2000s, while BMW flatly states that all its cars can use E10.

More modern future classics also escape the issue, since all new cars have been capable of using E10 fuels since 2011.

Clearly though, this doesn’t help owners of older cars, so what options do owners of traditional classics have? Well the good news is that the technology exists to upgrade the fuel systems to cope with the new fuel.

In truth, it’s good practice to renew ancient fuel lines as a precaution in any case. Modern fuel hose sold by a reputable supplier is rated for use with E10 (see Modifying for E10 below).

The commonly used SAE standard for fuel hose follows the J30/Rx rating, with the current J30/R9 being the accepted choice for modern fuels and rated at 100psi. The higher ‘R’ rating doesn‘t necessarily mean the hose is any better for ethanol fuels, though.

See my article on my experiences with fuel hose and ethanol fuel here

However, this may not be necessary for some owners, since the regulations require larger forecourts selling two grades of petrol to continue selling E5 fuel.

This will be offered only in the more expensive Super Unleaded grade however, which brings its own problems: even the bigger petrol stations often only have a single Super Unleaded pump, and in rural areas it may be hard to find a retailer large enough to stock it. Super Unleaded is also a more expensive fuel, with the price gap potentially set to widen further in time.

We’ll be keeping a close eye on further developments, but in the meantime the options for drivers of older cars are clear: if your car isn’t covered by the DfT online checker or is deemed unsuitable for E10, then you can either use the more expensive Super Unleaded or can update the fuel system and use a fuel stabiliser additive when the car is left for long periods.

Read on