Can you mix E5 and E10 fuel? Difference between new and older grade petrol - and where to find fuel checker

Everything you need to know about mixing 95 and 98 RON petrol during the fuel crisis, including whether it will damage your car

The current fuel crisis has seen drivers queuing for hours to try to fill up their cars.

On top of the current supply issues, drivers are also having to contend with confusion around the new E10 petrol, which is now standard across forecourts.

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E10 replaced E5 petrol at pumps at the start of September, becoming the standard 95 octane fuel sold as “regular” unleaded. E5 is now only sold as 98 octane, usually branded super or premium unleaded.

With drivers struggling to find any petrol, it has become a matter of filling up with whichever grade they can find but has raised questions about whether it’s safe to mix the two types of fuel.

Can I mix E5 and E10 petrol?

Although E5 and E10 have different compositions, the Department for Transport says it is entirely safe to mix the two grades.

Like mixing regular and super unleaded in the days of E5 petrol, mixing E5 and E10 in the same tank will not do any harm to your vehicle.

In its guidance on E10, the DfT says: “If your vehicle is compatible with E10 petrol, there’s no reason you can’t mix the 2 grades of petrol (E5 97+ and E10 95+). It’s perfectly safe to mix them in the same tank or fill up with E5 if E10 is not available.”

What is the difference between E5 and E10?

Both E5 and E10 are unleaded petrol but E10 contains a higher proportion of bio-ethanol - up to 10% compared with a maximum of 5% in E5.

This higher bio-ethanol content - obtained from renewable sources - helps to reduce the CO2 emissions from vehicles but slightly reduces their fuel efficiency.

Why has E10 petrol been introduced?

The Government says the introduction of E10 petrol will help reduce transport-related air pollution.

It estimates that changing to E10 will cut the UK’s CO2 emissions by 750,000 tonnes a year - equivalent to removing 350,000 cars from the road.

Can all cars run on E10 petrol?

The vast majority of modern cars can run safely on E5 or E10 but there are up to 600,000 older models in the UK which aren’t compatible with the newer fuel.

Any car built since 2010 is compatible with E10 fuel and most built since 2000 can also use the fuel without damage. However, some models from between 2000 and 2010 face problems using the fuel, as do hundreds of thousands of older and classic cars.

What if I have to use E10 in an incompatible car?

The current crisis means that some drivers may have to fill up with unsuitable fuel just to keep mobile.

The good news is that a single fill-up of E10 is unlikely to cause lasting damage to incompatible cars.

The damage caused by E10 to older cars largely comes about due to the long-term effects of the ethanol on perishable components, so a single emergency fill-up won’t do too much harm.

The DfT advises: “Using a single tank of E10 petrol in a vehicle that is not compatible should not be a major problem. Just make sure you fill up with the correct E5 (‘97+ octane) petrol grade next time.

Unlike putting petrol into a diesel engine, you shouldn’t need to drain the tank. On a one-time basis, your vehicle will not suffer engine damage as a result. Prolonged use of E10 petrol in a non-compatible vehicle, however, may cause harm and is not recommended.”