This is a story about E5 and E10 petrol, and you might ask ‘what’s it doing here?’ Why is Electrifying website bigging up fossil fuels?

Well, we’re not, but the immediate future of petrol, whether it’s E5, E10, or some yet to be brewed variety, is a source of concern to many hybrid and PHEV car drivers. After all, the oldest Toyota Prius is now heading for its mid-twenties, and there are plenty of decade old plus hybrids and plug in hybrids running around now that still need petrol and were sold before the new fuel was even on the horizon - think Vauxhall Ampera, its Chevrolet Volt identical twin, and the early petrol/electric BMW i3.

Will supping E10 bring them to a juddering halt? We’ll come back to that but let’s start with looking at why E10 exists in the first place.

The difference between E5 and E10 fuels relates to a change in the chemical cocktail -or blend- that these fuels are created from. This relates to the amount of renewable ethanol used in them. E5 has 5 per cent, E10 doubles that, and as a result is reckoned to cut CO2 -also known as greenhouse gas- because less of it is made from fossil fuel.

The government claims that E10 could reduce transport CO2 emissions by 350,000 cars or 750,00 tons a year -the equivalent making North Yorkshire a car-less county. Well, that’s the theory, and the politicians concede that vehicle-generated gases that have a negative impact on air quality won’t be reduced as E5 fuel is eclipsed.

PHEV's still need petrol occasionally

However, according to the Department for Transport ‘the production of renewable ethanol for blending with fossil petrol also results in valuable by-products, including animal feed and stored CO2.’ Given current geopolitical issues, that’s potentially good news.

Less good news is the fact that another by product of E10 is water, in the form of condensation which can in due course rot metal components in a car’s fuel system, notably fuel tanks, especially if your car sits around for weeks without being used. If you pilot an older PHEV and work hard to use its fossil fuel bits as infrequently as possible, this is something to bear in mind.

It’s also worth remembering that E5 will be much better to be used in petrol power tools such as lawnmowers which may have to sit around for a long time not being used. If you can’t avoid using E10, then consider buying a fuel stabiliser which will keep it fresher for longer and counteract the effect of the extra ethanol.

Some classic car owners have found that E10 eats rubber used for antique hoses, but any car built after 2011 should be able to cope with it, and plenty of the built before that won’t have a problem either, but if you’re not sure about your vehicle, key in its details at the official government website to find the answer.

Use your PHEV's engine infrequently and the E10 could cause issues

E5 petrol has a higher octane rating than E10 and actually burns with a little more efficiency than the newer fuel, so MPG from a tank of E5 will be slightly better than the equivalent amount of E10 - the Government claims an average 1 per cent efficiency reduction. However, this will vary according to the car and how you drive, so it's worth doing you own sums and experiments. This could mean that the extra economy you gain from using E5 'Super' unleaded makes it more cost-effective than using E10, especially at the current fuel costs where Super is around 5% more expensive. 

Some people reckon that the occasional tank full of E5 does older engines good, and if you like the idea of paying for fuel that doesn’t go off after a few weeks, making the occasional beeline to an E5 pump might appeal.

At present this is still a relatively straightforward thing to do. About three quarters of our filling stations still sell it, especially supermarket forecourts, but the law of diminishing returns mean that some smaller, often rural stations have already ditched it and this will be an accelerating trend as time passes.

E10 has been the standard fuel in EU countries for some time, has been the go to fuel for emissions testing since 2016, and arrived in the UK for general sale last summer. Northern Ireland is still waiting to welcome E10, but should make the switch at some point this year.

Have you tried E10? Did you notice any difference? Let us know!

E5 is much better for power tools which may be stored over winter