Can you mix E5 and E10 petrol in the same tank?

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Everything you need to know about mixing RON 95 and RON 98 gasoline, including whether it will damage your car and how to use a fuel tester on your vehicle

There is also still confusion about E10 fuel, which replaced unleaded E5 as the national standard almost a year ago.

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The new fuel type became the standard ‘regular’ petrol last September, with E5 continuing to be sold in super unleaded form at service stations that offer more than one fuel grade.

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Most modern cars can safely run on E10, now sold nationwide as regular 95 RON, but with E5 also available in a higher quality 98 RON, drivers have a choice of fuel to use. There are also some petrol stations that only carry E10 and others in rural areas that still supply ‘regular’ E5, raising questions about how safe it is to mix the two types of unleaded.

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Can I mix E5 and E10 petrol?

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

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

In its guide to E10, the DfT says: “If your vehicle is compatible with E10 petrol, there is no reason why you cannot mix the two types of petrol (E5 97+ and E10 95+). It’s perfectly safe to mix them in the same tank or top up with E5 if E10 isn’t available.”

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What is the difference between E5 and E10?

Both E5 and E10 are unleaded petrol, but E10 contains a higher percentage of bioethanol – up to 10% compared to a maximum of 5% in E5.

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Why was E10 petrol introduced?

The government says the introduction of E10 petrol will help reduce traffic-related air pollution.

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It is estimated that switching to E10 will cut the UK’s CO2 emissions by 750,000 tonnes a year – the equivalent of taking 350,000 cars off the road.

Can all cars run on E10 petrol?

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

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

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

Some drivers have claimed to have had a bad run when filling up with E10, but a single fill-up of E10 is unlikely to cause lasting damage to incompatible cars.

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Much of the damage E10 does to older cars is due to the ethanol’s long-term effects on perishable components, so a one-time emergency fill-up won’t do too much damage.

The DfT advises: “Using a single tank of E10 petrol in a non-compliant vehicle should not pose a major problem. Just make sure you use the right grade of E5 (’97+ octane) next time.

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Unlike putting gasoline in a diesel engine, you shouldn’t have to drain the tank. On a one-off basis, your vehicle will not suffer any engine damage as a result. However, prolonged use of E10 petrol in a non-compatible vehicle may cause damage and is not recommended.”

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