Is E10 fuel safe to use in my bike?

Back in March 2020 the Government published a consultation into proposals to make E10 the standard 95-octane petrol on UK forecourts – doubling the amount of ethanol allowed in petrol to the concern of many riders. Despite concerns raised by many respondents about the potential damage that E10 could cause to their vehicles the rules were pushed through into legislation and came into force in September 2021.

That was more than three years ago, and the kerbsides aren’t littered with broken vehicles struck down by damaged fuel systems. But that doesn’t mean E10 is suited for every bike on the road and there’s still no shortage of confusion over whether it’s safe to use or not.

What’s more, we’re now able to look back at the switchover and compare the ambitious claims of CO2 emission reductions associated with the changeover to E10 by then-Transport Secretary Grant Shapps and compare them with the real pollution statistics that came after the changeover. Has E10 really cut our carbon footprint?

What is E10 fuel?

Before we delve into the details, let’s recap the basics. Before the changeover, the standard grade for premium unleaded – which despite its name is the basic level of petrol on today’s forecourts – was 95-octane E5. Post September 2021, the octane rating remained the same, but the fuel became E10.

What does that mean? Well, the E stands for ethanol, which is ethyl alcohol derived from the fermentation of sugars. It’s the same alcohol found in drinks, burns pretty well, and unlike the refined fossil fuel that makes up the main component of petrol, it’s sustainable and renewable. The number is the maximum percentage of ethanol allowed in the petrol bearing the badge. So E5 can’t have more than 5% ethanol, while E10 can’t have more than 10% but must have at least 5.5% ethanol in its mix.

That’s an important point to remember - just because a fuel is badged ‘E5’ or ‘E10’ doesn’t mean it actually contains that much ethanol. An E5 fuel could have none at all, or it could have 5%. And an E10 might only have 5.5%, making it nearly indistinguishable from E5, or as much as 10%.

While it would be wonderful to know precisely how much ethanol was used by different brands, allowing riders to make an informed choice, the reality is that the ethanol content may easily change between batches of petrol, vary by area of the country, and even change with the seasons as fuel companies alter their recipes between winter and summer. However, since fuel companies aren’t likely to push the limits of what’s allowed, there’s a good chance that E10 will actually be somewhere safely in the middle of the range between 5.5% and 10%. Meanwhile, E5 – which remains on sale as a ‘Protection Grade’ fuel in the form of Super Unleaded, which is required to be stocked at petrol stations that sell more than one million litres per year and which have two grades. In extremely remote areas like the Scottish islands and Scilly Isles where no such large filling station is within easy reach, there’s exemption that allows them to stock fuel brewed to the old 95-octane E5 standard.

Has E10 reduced emissions?

When the plan to introduce E10 as the baseline grade for Premium Unleaded was first mooted it came accompanied with a baffling array of figures aimed at showing how the country’s carbon footprint could be reduced via the change.

The original consultation said that CO2 emissions from petrol vehicles would drop by around 2%, and ‘combined with an increase to overall renewable fuel targets, could cut overall transport CO2 emissions by a further 750,000 tonnes a year – the equivalent of taking around 350,000 cars off the road.’ If you’re thinking there’s a lot of uncertainty in those numbers, and that the figures are going to be hard to back up, you’re absolutely right.

Total petrol consumption is on the rise after years of decline, as car drivers – encouraged by taxation into diesels for a long period before a reversal of thinking – switch back to petrol-powered vehicles. In first half of the 1990s, UK drivers were buying more than 30 billion litres of petrol per year, with diesel at well under half that figure. By 2016, it was diesel that passed the 30 billion litres-per-year mark, while petrol sales were down to 17 billion litres. Petrol continued to drop – dipping to 13 billion litres in pandemic-struck 2020 – but has now climbed back past the 17 billion litres-per-year mark again while diesel is now the fuel in decline, dropping to 28 billion litres in 2024.

Surprisingly, all the way from 1990 to 2024 the total amount of fuel sold – diesel and petrol combined – has remained remarkably constant, as the rapidly-rising number of vehicles on the road is offset by their similarly great improvements in fuel efficiency. And while improvements in emissions standards mean that modern vehicles are vastly less polluting than their predecessors, total CO2 emissions haven’t changed much: in 1990, road transport was responsible to 110.8 million tonnes of CO2 emitted, and by 2022 (the latest available figure) that was down to 100.7, but still impacted by the reduced vehicle use that started in 2020’s Covid-19 pandemic. Why such a small change despite more than 30 years of development? Because the number of vehicles on the road, and more importantly the total mileage they cover combined, has risen substantially, from 255 billion miles in 1990 to 323 billion miles in 2022. In 2019, the last pre-pandemic year, the figure was higher still at 338 billion miles and total CO2 emissions were nearly identical to 1990’s numbers. Per vehicle mile, CO2 emissions have dropped from around 430g/mile to about 310g/mile.

When burnt, ethanol releases less CO2 than petrol, and since it’s a plant-based fuel, a proportion of that CO2 is reabsorbed during the production of the ethanol. Government documents said that “Using bioethanol in place of fossil fuels can reduce CO2 emissions by around 65% for an equivalent volume of fossil fuel” but given that E10 has only 5% more ethanol than E5, it’s actually only giving a benefit of 65% of that 5%. That means a litre of E10 might release around 3.25% less CO2 into the atmosphere when used, compared to a litre of E5. Oh, and because E10 can lead to increased fuel usage – it’s less energy-dense than E5, so you get fewer miles per gallon – the benefit is further eroded.

We can turn to government numbers again to see how little impact the E10 switch has had on direct emissions from vehicles. Looking at all road transport – petrol, diesel, hybrid etc – in 2019 (the last year in which vehicle use wasn’t skewed by the pandemic), 111.3 million tonnes of CO2 equivalent were pumped into the air as greenhouse gases by burning 35 million tonnes of fuel. That’s 3.18 tonnes of CO2 per tonne of fuel used (or 3.18 grams per gram of fuel, for that matter).  In 2022, the first full year of the E10 standard, the numbers were 100.7 million tonnes of CO2 from 31.6 million tonnes of fuel, which is 3.187 tonnes of CO2 per tonne of fuel. And it’s hovered around the same level – between 3.17 and 3.2 tonnes of CO2 per tonne of fuel – for since records started in 1990. Whether there’s any real saving in terms of the CO2 reduction in the production of ethanol compared to fossil fuels has also been the subject of several studies in the USA, which also has its own E10 legislation, with little agreement in their conclusions, as explained here by FactCheck.org.

A cynic might also point out that E10 offers slightly worse MPG than E5, forcing people to buy more of it, and the result is a tax windfall for the government. Petrol is taxed at 52.95p per litre, and even at the DfT’s conservative estimate that E10 reduces economy by 1% to 2%, that starts to add up. In 2022, road users bought over 17 billion litres of petrol – the vast majority of it E10. A 1% increase in fuel consumption means 17 million more litres sold, taxed at 52.95p, amounts to over nine million pounds. At 2% worse MPG it’s 34 million extra litres of fuel, increasing tax by over £18 million. There’s VAT on top of that, too, so the real tax revenue would be higher still.

What are the problems with E10?

Even if we put aside the hard-to-measure nature of the environmental impact of E10, the fuel itself poses potential problems for riders using it. Most of the issues are mechanical worries stemming from the fact that motorcycles haven’t been prepared to use E10 as long as cars have – theoretically every car since 2011 is E10-compatible – and motorcycles are generally longer-lived than cars, so the average age of bikes on the road is older, making them even less likely to have been manufactured with E10 in mind.

The problems with ethanol in fuel can be largely narrowed down to three areas. First, it’s a solvent, which means that it can damage some materials – particularly rubber hoses and seals in the fuel system – if left in contact with them for too long and the materials weren’t selected with ethanol fuels in mind. Even when your bike’s fuel hoses and components are rated to cope with higher levels of ethanol, as a solvent it can loosen dirt and corrosion in the fuel system, letting it flow into fuel filters, carb jets and injectors where it can cause blockages.

Second is the fact that, unlike petrol, ethanol is hygroscopic. That means it not only mixes with water but actively draws it in from the atmosphere around it. For most car drivers that’s not a problem – if you’re churning through a tankful every week, it’s not going to have time to absorb much water. But bikes that might spend all winter tucked away in a garage could suffer. At its worst, if ethanol fuel blends absorb enough water, they can reach a critical point called phase separation, when the water and ethanol separate to form layers in the tank – the petrol floating on top of the water. That can lead to corrosion and mean that the next time the bike is started it will be sucking something closer to water than petrol through its system, making it unhappy to start and run. What’s more, higher-ethanol fuel can become acidic over time, eating into materials like zinc, aluminium, copper and brass that might be used in the fuel system.

There are plenty of fuel stabiliser products available that claim to solve the problem and to guard against corrosion, but the easiest option, even if you use E10 day-to-day, is to use a lower-ethanol fuel like E5 Super Unleaded (which has a maximum of 5% ethanol, and could have much less, even none, depending on the brand and the particular blend being used), when you fill up before putting your bike away for winter.

Third, ethanol contains oxygen. That’s how it manages to reduce tailpipe emissions, but it also means that if you have an old, carb-fed engine there’s a chance it might run a little leaner on E10 than it did on E5. Bikes with modern injection tend to be fine, as they use oxygen sensors to monitor how lean the mixture is and compensate by adding more fuel if necessary.

Have people really been having trouble?

Of course, people have problems with their bikes sometimes. Particularly older ones. But is that rotten fuel hose a result of putting a tank of E10 in there or simply a symptom of age?

Mark Brewin, founder of BSD Performance in Peterborough, points the figure at modern fuels.

“E10 is destroying carbs,” he said, “It’s furring the needles up, blocking jets, eating rubbers. On injected bikes, too, the earlier ones in particular, we’re changing a lot more pumps and injectors. This fuel is horrible.

“Our advice is that if your bike has carbs, run E5 and put additives in if you’re storing the bike to stop it eating the carburettors. In fact, I wouldn’t use E10 in any bike.”

What happens if I put E10 in a bike that isn’t compatible with it?

In the short term, not much. E10 is petrol, even with the extra ethanol, so it’s not like accidentally filling with diesel. The bike will run on it, and because most of the issues associated with higher levels of ethanol are related to longer-term exposure, using the occasional tankful isn’t likely to cause a problem. Some riders report rougher running or significantly worse fuel consumption, while others swear there’s no noticeable difference.

It’s with extended use, whether because you’re consistently running the bike on E10 or storing for a long period with E10 in the tank and fuel system, that problems like corrosion or damage to gaskets, hoses or seals might emerge. If you have no option but to use E10 – for example if you’re running low and the nearest garage doesn’t stock E5 – and your bike isn’t compatible, the best advice is to put in only as much as you need and to dilute it with E5 Super at the earliest opportunity.

How long will E5 remain available?

One of the big fears is that the shift towards increase ethanol means that the lower-ethanol E5 Super Unleaded that many of us use to avoid the potential hazards of E10 will eventually disappear from forecourts.

Back when the legislation was drawn up to make E10 the standard grade for unleaded in 2021, the government committed to ensuring that E5 Super will be stocked on all forecourts that have at least two grades of fuel, dubbing it ‘protection grade’ for older vehicles. The plan at the time was to review the situation in five years – which means 2026 – but that any review would “examine if there’s a viable and widely available alternative to ensure suitable low-ethanol fuel remains available for older vehicles and other petrol-powered machinery that require it,” and the government’s document said “We would like to reassure owners of such vehicles or equipment that, without such a grade becoming available, it’s highly likely that the E5 protection grade would continue to apply.”

Is my bike is E10 compatible?

As a rule of thumb, most bikes made in the last decade or so should be compatible with E10 and many far older bikes were also designed to use it. Even before it was mandated in the UK, E10 and even some higher-ethanol mixes have been in use in other countries – Brazil has used a minimum of 10% ethanol in its petrol since 1976, and today uses E25 as its standard fuel, for example – so manufacturers have decades of knowledge on how to make bikes work with E10 and how to prevent damage.

To be absolutely sure, there are several other checks you can make. Your owner’s manual should confirm what fuel grade is needed, and you may even find a sticker on or near the fuel filler that repeats those requirements. Over and beyond that, the Government has its own dedicated E10 compatibility check website - www.gov.uk/check-vehicle-e10-petrol - which includes most common brands and models, but is far from complete. A more comprehensive listing can be found on Dutch website www.e10check.nl, although you might need to your browser’s translation function to understand what it says. For complete peace of mind, there’s always the option of speaking to your dealer or your bike’s manufacturer or importer to confirm whether they’re happy for it to run on E10. However, even with compliance, remember the short shelf-life and water-attracting properties of E10 if you’re storing your bike over winter and consider either adding a fuel stabiliser or a tank of E5 Super Unleaded before putting it away.

Can I use E5 fuel in an E10 bike?

Absolutely. Reducing the ethanol content isn’t going to do any harm at all. After all, E10 rules only say that the fuel can have a maximum of 10% and a minimum of 5.5%, so there’s a good chance that a lot of ‘E10’ is within a percentage point or two of ethanol content compared to some E5 fuels.

Can you use E10 in a two-stroke?

The issues around E10 are much the same in a two-stroke engine as in a four stroke – the potential corrosion and incompatibility of some rubber components being the main concern – but there are reasons why two-stroke owners might be more likely to want to stick with E5 Super.

The first of these is simple: most two-stroke street bikes on the road today are likely to be pretty old. Unless you’ve got your hands on a Langen Two Stroke or one of the handful of road-legal two-stroke enduro models that have persisted into more recent years, you’re probably riding something from the 70s, 80s or 90s if you’re a two-stroke user. As such, they’re less likely than more modern bikes to use the ethanol-friendly materials in their fuel systems. It’s the same as four-strokes: check with the manufacturer or handbook to see what fuel is specified before using E10.

On top of that, nearly all two-strokes are carburetted rather than injected, which means they’re not equipped to automatically adjust for the fact that E10 fuel runs slightly leaner than E0 or E5, and running a two-stroke too lean can be bad news. That means you might need to tweak the tune to getting it running a bit richer if you’re opting for E10.

If you’re riding a two-stroke on the street it’s a pretty clear indication that you’re not too concerned about penny-pinching at the pumps, so the easiest way to avoid any problems if you’re unsure about which fuel to use is to stick to E5 Super while it’s still available.