What to do if you put the wrong fuel in your car

If you’ve put the wrong fuel in your car, don’t start the engine. Here’s what to do next and how to avoid costly damage if you’ve used the wrong fuel.

Putting the wrong fuel in your car is more common than you may think. In fact, around 150,000 UK drivers fill up with the wrong fuel every year, according to the RAC.

The important thing is not to panic – and don’t start the engine. Driving with the wrong fuel can cause serious and expensive damage, so the sooner you realise what’s happened, the better.

So, what should you do if you’ve put the wrong fuel in your car? Here’s everything you need to know, from what to do at the petrol station to what happens if you’ve already driven away.

Remember, you can buy a brand new or used car right here on Carwow. And you can sell your car, too. We’re here to help you through every step of your car-changing journey.

What to do if you’ve put the wrong fuel in your car

1. Don’t start the engine

If you realise you’ve used the wrong fuel before starting the car, leave the engine switched off and don’t turn on the ignition.

If you’re at a petrol station, tell a member of staff what has happened and, if it’s safe, move the car away from the pump. You’ll need to push it into a parking space or another safe area, so you may want to ask bystanders for help.

2. If you’ve already driven away

Stop as soon as it’s safe to do so and switch off the engine. Don’t continue driving to reach a garage or petrol station, as this will circulate the incorrect fuel through the system and increase the risk of damage.

If you’re on a busy road and can’t move the car, stay somewhere safe and wait for assistance.

3. Call for assistance

Contact your breakdown provider or a specialist misfuelling service and explain what has happened.

A recovery specialist can usually drain the incorrect fuel from the tank. If the engine hasn’t been started, this may be all that’s required before refilling with the correct fuel.

If you’ve driven the car after misfuelling, it may need to be inspected for damage. Your recovery provider can advise whether it’s safe to drive or whether the car needs to be taken to a garage.

What happens if you put petrol in a diesel car?

Putting petrol in a diesel car can cause serious damage, particularly if you start the engine.

Diesel fuel provides lubrication for important components in a diesel fuel system, including the high-pressure fuel pump. Petrol has different properties and can reduce this lubrication, increasing friction and potentially damaging the fuel pump, injectors and other components.

The risk of damage increases once the engine is running because the contaminated fuel is circulated through the system.

If you’ve started the engine, you may notice:

• Loss of power
• Rough running or knocking
• Excessive exhaust smoke
• An engine warning light
• The engine cutting out
• Difficulty restarting

What happens if you put diesel in a petrol car?

Putting diesel in a petrol car is generally less likely to cause serious damage than putting petrol in a diesel, but you should still stop driving as soon as possible.

Diesel doesn’t burn correctly in a petrol engine and can contaminate the fuel system and spark plugs. This can cause misfires, rough running, loss of power and the engine to cut out.

Continued driving can also cause damage to components such as the catalytic converter.

You may notice:

• Engine misfires
• Rough running
• Loss of power
• Excessive exhaust smoke
• The engine cutting out
• Difficulty restarting

What happens if you put E10 in a car that isn’t compatible?

E10 is now the standard 95-octane petrol grade in the UK, and almost all petrol cars on the road can use it. All new cars built since 2011 are compatible with E10, although some older cars are not.

If you’re unsure whether your car can use E10, check the owner’s manual or the government’s E10 compatibility checker.

If your car isn’t compatible and you accidentally fill it with E10, there’s no need to panic. Using a single tank of E10 in a non-compatible vehicle should not cause engine damage. You should switch back to E5 petrol at your next opportunity.

E5 petrol remains available as a higher-octane ‘super’ grade at filling stations that offer it.

Fixing a misfuelled car

In most cases, the first step is to drain the incorrect fuel from the tank and fuel system. A breakdown provider or specialist misfuelling service may be able to do this at the roadside.

If you haven’t started the engine, draining the fuel should be all that’s needed.

If you have driven the car, a mechanic may need to inspect the fuel system for damage. Depending on the type of fuel and how far you’ve driven, components such as the fuel pump or injectors may need to be repaired or replaced.

The cost can therefore vary significantly depending on the car, the fuel involved and whether any damage has occurred.

Is misfuelling covered by insurance?

It depends on your policy.

Misfuelling isn’t automatically covered by every car insurance policy, although some insurers offer specific misfuelling cover or provide it as an optional extra.

Check your policy documents or contact your insurer to find out whether you’re covered for fuel draining, recovery and any resulting repairs.

It’s also worth checking your breakdown policy, as some providers offer dedicated misfuelling assistance.

Misfuelling a car FAQs

I’ve only put a few litres of the wrong fuel in my car. Will it be okay?

Don’t assume the car is safe to drive simply because you’ve only added a small amount of the wrong fuel.

The risk depends on the type and amount of incorrect fuel, as well as whether the engine has been started or the car has been driven. Leave the engine switched off and get professional advice.

Will breakdown cover pay for misfuelling?

It depends on your policy. Some providers offer dedicated misfuelling assistance, which may include draining the incorrect fuel and supplying enough of the correct fuel to get you moving again.

Check your policy before assuming you’re covered.

Will my car insurance cover misfuelling?

Not necessarily. Some policies include misfuelling cover, while others offer it as an optional extra.

Check your policy documents or speak to your insurer to find out what’s covered.

Will misfuelling invalidate my car warranty?

Not necessarily, but check the terms of your warranty.

Damage caused by using the wrong fuel may not be covered under the manufacturer’s warranty because it isn’t considered a manufacturing fault.

How much does it cost to fix a misfuelled car?

There’s no standard cost for fixing a misfuelled car. If you haven’t started the engine, draining and refilling the tank typically costs around £120-£300, according to Misfuelled Car Fixer.

If you’ve started or driven the car, damage to the fuel system can push repair costs into the thousands, potentially £1,500-£5,000+. The final cost depends on the vehicle, fuel involved and extent of any damage.

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