What's misfuelling? What should I do if I fill up with the wrong fuel?

Published on 14 December 2023

Putting the wrong type of fuel in your car is known as misfuelling. You’ll be forgiven for thinking it’ll never happen to you but, trust us, it can happen to anyone! In fact, it’s estimated around 150,000 drivers misfuel in the UK every year.

If it happens to you, there’s no need to panic, but it’s important to know what to do. So, what should you do if you end up with petrol in a diesel car or diesel in a petrol car?

Don't start your car

If you've already driven off before realising the mistake, stop somewhere safe.

Call your breakdown or insurance provider

Your policy may cover misfuelling so get in touch and follow their instruction.

Drain your fuel tank

If you have breakdown cover, they can come out and drain your fuel tank.

It’s more common for petrol to be put into a diesel car, the petrol nozzle is smaller and will fit into the diesel tank. This can be a serious problem as diesel cars use the fuel to lubricate the engine and reduce wear and tear, but petrol’s corrosive and your engine’s not designed to withstand it.

The damage can be far-reaching and could lead to you needing to replace the whole fuel system, which is as expensive at is sounds.

If you put petrol in a diesel car and start the engine before you realise the mistake, there can be telltale signs such as a noisy engine, struggling to start the engine or the engine doesn’t stop once its running.

It’s best to avoid starting your car after you misfuel as it can prevent further engine damage.


Yes, unfortunately this is also a more common problem than you might think. While the diesel nozzle is bigger, making it harder to fill a petrol car with diesel, it’s by no means impossible.

If this happens, the diesel will clog the fuel system and stop the car from starting. The fuel tank must be drained to protect your car from any damage.

E10 fuel has 10% renewable ethanol, it reduces CO2 emissions associated with petrol cars. About 95% of petrol cars can use E10 fuel -  check if yours is compatible.

If your car takes petrol and you accidentally fill it with E10 fuel, there may be no harm if your vehicle’s compatible. If it’s not, there’s no cause alarm, just make sure you fill it with E5 petrol once you’ve used up a third of the tank.

It’s another story if your car’s a diesel, however. Filling up with E10 can have the same negative impact on your engine as misfuelling with regular unleaded petrol.

  • Don’t get distracted when you’re at the pump.
  • Check the label of the pump you’ve picked up.
  • Your car may have a sticker inside the fuel cap with the name of the fuel. If it doesn’t, add one yourself to remind you.
  • Before you start filling, check the labels on the pump and fuel cap are the same.
  • Installing a misfuelling prevention device or cap may be useful if you regularly use different cars with different fuel.

Allianz Car Insurance covers misfuelling so, if you put the wrong fuel in your car and start it by mistake, we cover the damage to the car’s engine and drain & flush your fuel tank.*

*You may have to pay an accidental damage excess – we’ll tell you how much that is when you make a claim.

It's easier than you might think to fill up with the wrong fuel, especially when you’re still learning to drive. But, whatever happens, it’s good to know that with Allianz Car Insurance you’re in control 24/7. So, whether you put petrol in a diesel or diesel in a petrol, you can rest assured we’ve got you covered.

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