The UK has switched to E10 petrol. Here’s what it is and what it means

As you might have seen, the UK has introduced E10 petrol as the standard fuel available at the pump. While an episode of Neighbours has a statistically higher chance of changing your life, E10 fuel nonetheless has a lot of people wondering what it is and why we’re now using it. So let’s answer the big questions about E10, so we can get back to answering the real question here: why does anyone watch Neighbours?

What is E10 petrol?

It’s a blend of ethanol and petrol, with the ‘E10’ part referring to the maximum amount of ethanol allowed in the mix – 10 per cent. It’s far from the only standard for mixing drunk sauce and dino juice, with countries all over the world using blends from four to 95 per cent.

The blends differ due to differing legislation in various countries, as you’d expect, but it’s also based on supply of ethanol-producing crops. So Brazil, with acres upon acres of sugarcane, runs higher ethanol-petrol blends, and even uses 100 per cent booze in some cars. America leverages its huge corn crops to make delicious cornbread and much less delicious ethanol-blended petrol.

Really, do not drink petrol. Or straight ethanol, for that matter.

Why use E10 petrol?

There are a few reasons. The original idea is to supplement regular petrol so we use less of it; the other is to do with carbon dioxide emissions.

The US of A is quite fond of blending ethanol with its petrol, supplementing the fossil-based fuel with some farm-fresh booze in order to reduce its dependence on foreign oil. But that’s America, where farm subsidies prop up corn production to the point that they use it as a sweetener instead of sugar. And for making each drop of petrol go further – handy when you’re driving a Yank-spec behemoth.

The other argument is to reduce carbon emissions. The idea is that ethanol has less carbon than petrol – just two carbon atoms per molecule to petrol’s average of eight – so burning it will release less carbon dioxide. And that’s perfectly reasonable science. But that really only tells a little bit of the story.

Compared to petrol, ethanol has a lower energy density. Think of it like the difference between a salad sandwich and a donut. Both are food, but one has a lot more energy per bite, and also goes much better with a cup of coffee. But that might be beside the point.

In an engine, burning a less energy-dense fuel means that you need to burn more of it to get the same amount of power. This doesn’t mean that you’ll lose power if you use E10; rather that your fuel economy will drop as your car’s engine computer fiddles with fuel-air ratios to get the best stoichiometry (a fancy-pants term for the ideal mixture). So while the carbon count goes down with ethanol-blended petrol, fuel consumption goes up.

The question of whether that negates the point entirely is one that we’re not touching with a barge pole, because – much like almost any argument these days – it gets really political, really quickly, and then descends into ad hominem attacks until we lose what little faith we still have in humanity. Suffice to say that the lower fuel economy certainly mitigates the benefits to some extent.

What is the difference between E5 and E10 petrol?

E5 petrol has a maximum of five per cent ethanol blended with the petrol. E10, as you might expect, has a maximum of 10 per cent ethanol. E5 won’t necessarily have exactly five per cent, nor is E10 guaranteed to have exactly 10, but it is a hard limit.

That way, if your car will work with E10 (and the majority of petrol-powered cars do), you won’t accidentally use fuel with higher concentrations of ethanol, which can cause problems in cars that aren’t made for it.

Can I blend E5 and E10?

If you currently have a bit of the old E5 in the tank and fill up with E10, there’s not going to be a problem at all – if your car can handle E10 fuel. If it can handle E10, it can handle anything from zero to 10 per cent ethanol without a hiccup. Unlike us.

Are there any problems using E10?

Apart from what we’ve already mentioned in terms of fuel economy, you can run into issues depending on the kind of car you drive. If you drive an electric car, for instance, you’ll find that it runs exceptionally poorly if filled up with E10 petrol. Or regular petrol, for that matter.

Generally speaking, most modern cars that run on 95 octane fuel today will run on 95 octane E10 fuel tomorrow without the slightest hiccup. As we said before, sensors will figure out the quality of the fuel, the engine computer will make an on-the-fly adjustment to fuel-air mixtures and so on, and you’ll drive along none the wiser.

With that said, ethanol is hygroscopic, which is a pocket-protector way of saying that it readily takes up water. In fact, if you poured 50mL of pure ethanol into a glass and then added 50mL of pure, distilled water, you’d only end up with about 96mL of solution (and a pretty rubbish cocktail), due to the fact that water and ethanol get in close and form bonds, much like people do after exposure to ethanol.

The problem for your car is that water – outside of your radiator and wiper bottle – is generally a bad thing, rusting and corroding delicate fuel system and engine parts that were never designed to come anywhere near water. And if you drive infrequently, extra ethanol in your tank will absorb extra water from the atmosphere and separate the fuel into straight petrol and an alcohol-water mix. The ethanol-water mix will sink to the bottom of the tank, and then, if you ever run low on petrol, you’ll pump water-diluted alcohol into your engine. And no one likes watered down booze.

Alcohol itself is no great friend to engines, either. If you cast your mind back to the 24 Hour Britcar race on Top Gear TV, you’ll remember all the issues the team had with the alcohol content in their farm-fresh biodiesel – the methanol that was used to make the fuel ate the seals in the fuel pump, then the fuel lines themselves.

On the other hand, if you have a car where the fuel tank, pump and lines (and a few other things besides) are made for ethanol blends, you’re laughing.

Is E10 petrol more expensive?

Not generally, no. Australia’s had E10 fuel for years, and it’s reliably been the cheapest option at the bowser since then – despite having a higher octane rating than the cheapest straight petrol option.

And as it’s replacing the standard 95-octane petrol that’s currently available in the UK – which already contains up to five per cent ethanol – it’ll likely remain the cheapest option at the pump. With that said, E10 petrol has less energy per litre than E5 or petrol with no ethanol, so, like we said, your car will almost certainly burn more of it. Which then means you have to fill up more often. So it’ll probably end up costing more, by dint of the fact that you’ll have to use more.

Is my car compatible with E10 petrol?

Generally, yes. Ethanol-petrol blends have grown in popularity over the past two decades, and anything made after 2011 should (what a wonderful caveat that is) accept E10 without worry. For a great many manufacturers, that worry-free timeline extends back to the early Nineties and even mid-Eighties. For some manufacturers, it’s as simple as ‘anything with fuel injection’, due to ethanol’s tendency to trash carburettors in a number of un-fun ways.

To demystify things a bit, the UK government has a site where you can check if your car can handle E10 fuel... with the caveat that it “will not be liable for any damage to your vehicle as a result of you using this service”. So that’s reassuring. That said, you can still buy the pricier 98 octane dino-juice for at least the next five years, if you’d prefer to pay more to rest a bit easier.

If you ride a motorbike, be wary of ethanol blends. While most major manufacturers have taken steps to ensure E10 compatibility, other (and older) bikes, and some mopeds, won’t run properly, so you should stick to fuel with as little ethanol as possible. And, like cars, this goes double for anything with carburettors.

Bikes likely can run on E10, if you want to – or have to. But, given most motorcyclists tend to cherish their bike – and that bikes generally use hardly any fuel – we’re tipping most riders will stick with the good stuff.

Can I use petrol with more ethanol, like E25, E50 or E85?

Not unless your car specifically says so, no. In cars like these, generally known as flex-fuel vehicles, the engine, fuel system, exhaust, sensors and computers are all made (or adapted) to deal with high-ethanol fuel. Any bare metal or rubber is taken out of the fuel system, for instance, so the booze won’t corrode it, and the rate, flow and spacing of fuel injection changes. There’s lots more, but we’ll be here all week listing it.

There are benefits to high-ethanol fuels, if your car’s set up to take them. For instance, both the Koenigsegg Jesko and SSC Tuatara (among many others) make oodles more power on E85 than they do on regular fuel, because ethanol has a huge cooling effect and resists detonation (knocking, pinging, engine exploding). So the engine control unit can advance spark timing and so on to the point that’d completely lunch an engine running on regular petrol, resulting in a Tuatara that makes 400bhp more on E85 than it does on pump gas, as the Americans call it.

When does the UK start using E10 petrol?

It’s already started in mainland UK – the Government announced that E10 would replace the standard 95 octane fuel (which already had up to five per cent ethanol) in the summer of 2021. If you’re from Northern Ireland, you’ll see it in early 2022. Or perhaps more likely, you’ll just fill up with 95 octane, just like before, and continue on with your life.

Really, it’s only going to be a big deal if you drive something specific or ride a motorbike. In that case, just head for the pricey stuff and watch your bank account drain in real time, like we do every time we fill up.