Is E10 fuel bad for your car?

Here’s a question we hear quite a bit at CarsGuide: Is E10 bad for your car and does E10 fuel damage engines?

There’s no simple answer, because some cars are quite happy on E10 fuel, while other are not. Get it wrong, and you could damage your car’s engine and fuel system. So what’s the real story?

Let’s start with the basics: What is E10 fuel?

The E in E10 stands for ethanol. And the 10 is the percentage per litre of fuel that is ethanol. Which means E10 is also 90 per cent normal petrol.

So why make E10? Because it’s a way of using less fossil fuel (ethanol is alcohol largely derived from crops, so it’s sustainable and, more correctly, called bioethanol) and also reduces tailpipe emissions of the greenhouse gas by-products of burning petrol.

E10 is readily available in most service stations around Australia (and is used in many countries) and it’s usually a few cents cheaper than standard ULP.

That means it can be cheaper to fill up with E10, but the reality is that the same engine running on E10 or ULP will use a little more fuel on E10. So the advantages relate mainly to E10s sustainability and lower tailpipe emissions.

Many people think a lack of octane is the problem with E10, and that’s why it can hurt some engines. But it’s not. The truth is E10 has an octane rating of about 94 compared with the 91 of standard ULP (higher is better, generally speaking).

So, what is the problem with E10? It’s all to do with the fuel systems of some cars and what they’re made from. Ethanol can harm some types of rubber and plastic on contact and, if your vehicle uses those materials, then E10 is a no-no for you.

Over time, the ethanol will attack those rubber and plastic fittings and cause them to fail, potentially leading to a fuel leak, or at least a break-down of the fuel system’s integrity and efficiency.

In some cases, the ethanol content can also cause corrosion in some metal parts of the engine, typically the carburettor on older vehicles.

Generally – very generally – speaking, it’s older cars that have the most problems with using E10. But different carmakers from different countries use different technologies in their fuel systems, so this is by no means a hard and fast rule.

Also, a car’s ability to use E10 or not has no relationship to its ability to run on ULP versus old-fashioned leaded fuel. The requirements to operate on each fuel are completely independent.

So, what are the other common questions? Well, is E10 unleaded is one. Yes it is, because it’s made from 90 per cent ULP (with that 10 per cent dash of ethanol, remember).

And what about: Is E10 the same as 91? Well, yes it is, in a way, because it will run fine in any engine designed for 91 octane ULP as long as the same car is also E10 compatible.

It’s worth noting, however, that the octane rating of E10 is 94, so cars that need 95 or even 98 octane fuel won’t be suitable for E10.

For a lot of car owners, the real issue comes down to a question of E10 vs 91 ULP. And, again, if the car is designed to cope with an ethanol-blended fuel, then using E10 will probably save you a dollar or two at the pump, but might cost you those same dollars in terms of overall fuel economy. Which means the real difference is in the sustainability of ethanol and the emissions reduction when running on it.

The other big question is can I mix E10 and 91? Yes, you can. Half a tank of each won’t hurt an E10-compatible engine at all, and you can freely change back and forth between the two fuels as prices and availability allow.

So, how do you tell if your car can use E10 or not? The first thing to do is check the owner’s manual. There should be a chapter on fuelling your car, and this is where the relevant info should be.

If it’s an older car built before E10 was a thing here, or the handbook is missing, there are several online reference sources including this one from the NSW Government - https://www.nsw.gov.au/driving-boating-and-transport/e10-fuel/e10-compatibility-check

As for where to find E10 fuel, you really just need to find a service station as the stuff is widely available. Failing that, the major fuel companies operate websites with E10 (and other fuel type) locators.