What is E10 fuel and should I be putting it in my car?

E10 fuel, available in Northern Ireland already, is coming to the Republic of Ireland this year

Irish motorists are already starting to ask questions about the incoming use of E10 unleaded petrol here. The new fuel blend is due to be introduced to Ireland this year, according to the Department of Transport, and it will come to the island of Ireland sooner, with an introduction in Northern Ireland due in November.

E10 fuel contains a higher level of bioethanol – an alcohol-based fuel made from distilling plants – than current E5 fuel. The 10 refers to 10 per cent, the level of bioethanol in the fuel with the remaining 90 per cent made up of standard unleaded petrol.

According to the Department of Transport, switching to E10 fuel could see “an estimated potential tailpipe carbon savings of between 330,000 and 550,000 tonnes of CO2eq from now to 2030.” That’s because, in theory, if you make some of your petrol from plants, those plants have already absorbed carbon dioxide from the air when they were grown. Converting them into fuel and burning that fuel means that you’re only releasing carbon already removed from the atmosphere. The idea is that the fuel becomes carbon neutral.

Which sounds like a wonderful idea, so what’s the problem? The problem is that bioethanol isn’t chemically the same as regular petrol, and it can actually be corrosive to some parts of a car’s engine and fuel system. Parts such as rubber fuel lines and seals, gaskets, plastics and even some metals are vulnerable to E10′s corrosive potential.


The concern is that running cars, especially older models, on E10 could cause damage or worse, particularly among owners of classic cars.

Thankfully for the majority of us that’s simply not going to be an issue.

Every new car sold in Ireland since 2011 has had to be compatible with E10 fuel, as per European Union regulations.

“In the US they’ve had E10 since the 1970s and for the last 20 years they’ve had nothing but E10. That’s way more than a billion cars running on it of every make, model and age imaginable, and there hasn’t been a single claim or case involving E10. Not one. And the US is a litigious place” James Cogan told The Irish Times.

Cogan is an industry and policy adviser with Ethanol Europe, so obviously has his reasons for advocating bioethanol fuel. Nonetheless, he’s adamant that there’s no need for Irish motorists to worry. “Ireland has already been running on E5 for a decade and it’s been all good. It’ll be all good too, going to E10.”

Cogan is also, as it happens, a member of the group that’s most worried about E10 fuel – classic car owners. The older the car, the more vulnerable it is to E10-related damage, but the general feeling among Irish classic car owners seems to be that those who regularly maintain and look after their cars are not going to have any worries.

Those that are in danger are those who choose to invest their money in classic cars, but don’t invest time in learning about the cars themselves. It is they who may, accidentally, damage their own investments by using the wrong fuel.

Cogan, who owns a 1955 MG TF, told The Irish Times: “A normally maintained vintage car will have no issues, irrespective of the percentage of ethanol in the petrol, while an old car with perished hoses and seals will present problems, again, irrespective of the fuel blend. There are no mods needed to my old car for E10. It was restored to original factory condition in the mid-1980s and is still pretty much good as new. I have it checked out every year. If someone has ancient hoses and seals they should replace them anyway, but not on account of the fuel blend change.”

One worry, which seems more persistent than those over actual damage or fire breaking out, is over E10′s fuel economy.

The bioethanol component of E10 has a lower calorific content than standard unleaded fuel, so you have to burn more of it to get the same power output. That can lead to higher fuel consumption, and once again in this instance it’s older cars, especially those with smaller, theoretically more frugal engines which are most likely to suffer from this.

Officially, the difference is supposed to be only about 1 per cent compared with running on E5 fuel, but anecdotally some car owners have reported significantly higher fuel consumption when running on E10.

Other issues may include starting issues in cold weather, or ‘vapour lock’ stalling on very hot days, as ethanol vaporises more easily in heat than petrol. For those with a car that simply cannot be converted to run on E10, some filling stations will retain supplies of E5 fuel, but that is likely to be limited to ‘super unleaded’ blends which will be more expensive.

Equally, many smaller filling stations – which have only two tanks; one for diesel and one for petrol – will have to stock only E10 and nothing else, forcing those customers to shop for fuel elsewhere.

There are also concerns about E10′s effects on fuel economy. Because E10 is less energy-dense than normal unleaded petrol, you have to burn more of it to achieve the same power output, which can mean worsening fuel economy.

Figures for how much worse vary, from an estimate by the AA of 1.6 per cent, to the US Environmental Protection Agency, which reckons that you’ll burn 3-4 per cent more fuel when running on E10. UK-based insurance comparison site GoCompare calculated that the lower efficiency of E10 will add about €350 to an annual fuel bill.

Previously, when ethanol-based E85 fuel was tested in Ireland in the early 2000s, the higher rate of use was more than offset by the fuel’s cheaper pump price. With E10, though, you’ll still be paying the same price per litre.

Neil Briscoe

Neil Briscoe

Neil Briscoe, a contributor to The Irish Times, specialises in motoring