E10 petrol: how will the switch affect your car?

From today, fuel retailers will be made to adopt a new petrol formula to reduce emissions. We explore what it means for motoring

"Petrol is changing,” according to the government, and many of us will need to pay attention. It’s all about E numbers: never mind which chemicals are in your packet of Angel Delight, it’s the ingredients keeping your car going that you need to know, and the new concoction is called E10.

Here’s the E-based backstory. In order to make conventional fuels less bad, it was decided to blend in some renewable content such as biodiesel and ethanol. This is nothing new: it has been going on with petrol and diesel in the UK for the past 10 years. Apparently, blending renewable fuels in this way has contributed to a CO2 emissions reduction equal to taking more than a million cars off the road.

The labelling has never been terribly clear, but presently petrol is called E5 (up to 5% ethanol) and diesel B7 (up to 7% biodiesel).

The label we now have to look for on the pump reads E10. This is a biofuel made up of 90% regular unleaded and 10% ethanol, hence the name.

Ethanol is an alcohol-based fuel that’s produced from a range of plants, including sugar cane and grains. The upside is that, unlike regular unleaded petrol, ethanol actually absorbs CO2, partially offsetting greenhouse gas emissions.

The SMMT estimated that 92.2% of the petrol-engined vehicles in the UK are compatible with E10. Since 2011, all new cars sold in this country have had to be E10-compatible.

Vehicles manufactured from 2019 onwards usually have an E5 and E10 label close to their fuel filler caps, showing which fuels they can accept. So what’s the problem? Well, drivers of cars registered before 2002 have been advised not to use E10 in their vehicles, because problems have been reported.

Research carried out by our sister title What Car? revealed that E10 is potentially less efficient than the current E5 blend of petrol, with the problem being worse in smaller-engined vehicles. Drivers of shopping cars would end up filling their cars more often, which isn’t the point of owning a small car with a tiny engine.

Certainly, proper classics that are 40 years old or more will all have problems, but so will modern classics from the 1990s, a lot of cool motorbikes, stupid mopeds and most likely petrol lawnmowers. It couldn’t be easier to check whether you need to worry, of course (simply visit gov.uk/check-vehicle-e10-petrol), but what are the main downsides for owners of older cars?

E10 petrol’s higher bioethanol content is corrosive to rubber parts, gaskets, seals, metals and plastics, which causes engine damage, so it could dislodge deposits in older engines and fuel systems, causing blockages. It should only be used with expert advice, which means pretty much never.

What owners of vulnerable cars can do is source replacement engine components made with ethanol-compatible materials. Otherwise, the quick fix is to use the higher-octane 97-99 Ron ‘super unleaded’ E5 petrol, which is expected to remain available at most fuel stations after E10 comes into use.

The Petrol Retailers Association has confirmed that “E5 will still be available in five years time, but only as the protection grade in ‘super’. It will be reviewed in five years time.”

Super unleaded comes at a price, however. Recently, it has cost up to 12p more per litre than regular unleaded, which is around £6 to £7 more per tank.

If you make a mistake at the pumps and brim your older car with E10, all is not lost. Unlike the fuel-tank draining consequences of a petrol-diesel misfuel, simply dilute it with E5 from then on and it should be fine. But don’t make a habit of it, say the manufacturers, including Shell.

The bottom line on all of this – and whether you agree that “petrol is changing for the better” – will probably be pretty dependent on whether your car is E10-friendly or not. Best head to Westminster’s website post-haste, then.

*How E10 petrol can affect pre-2002 cars*

*Winter worries*

Higher ethanol content in petrol can make it harder to turn over an engine from cold.

*Vapour lock*

Ethanol’s higher volatility can contribute to vapour lock (petrol becoming gaseous) when operating temperatures are higher, causing stalling.

*Leaks*

Ethanol’s high solvency can cause problems with many seal and gasket materials that are used in fuel systems, as well as with fibreglass resins.

*More leaks*

Besides a risk of fuel leaks, rubbers and resins can get partially dissolved, producing deposits that could foul carburettor jets.

*Corrosion*

Ethanol can become acidic and cause corrosion of aluminium, zinc and galvanised materials, as well as brass, copper and steels coated in lead or tin.

*READ MORE*

*Government plans E10 petrol roll-out from September 2021*

*More than 600,000 cars incompatible with proposed E10 introduction*

*Analysis: What future is there for rural petrol stations?*