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05 Sep 2019
Jamie Gibbs Jamie Gibbs

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

Graphic showing new labels for petrol (E5) and Diesel (B7) pumps


Important: If you’ve used the wrong fuel, do not switch on the engine or put the key in the ignition.

The Department for Transport has announced that all fuel pumps are to be given new labels to make it clear which fuel you should be using in your car.

There's no change in the fuel itself - just the labels.

Ironically, this may cause even more confusion in the short term as motorists used to seeing 'unleaded' and 'diesel' are now greeted with 'E5' and 'B7'.

And with that, it may happen that you choose the wrong pump and accidentally put diesel in your petrol engine. But worry not - there's a way out of this.

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New petrol and diesel pump labels explained

The new labels are designed to tell you exactly what you're putting into your car.

First is the shape on the label. A circle means petrol, and a square means diesel.

The letter on the label tells you what renewable fuel source has been added to help with the environment.

E means ethanol, and B means biodiesel.

Finally, the number tells you what percentage of that renewable fuel is mixed in.

E5 means your petrol is made up of 5% ethanol, and B7 means your diesel is made of 7% biodiesel.

As well as fuel pumps, the government plans to have these labels put on the fuel caps of cars from April 2020.

What happens when you put petrol in a diesel engine?

As well as powering the car, diesel acts as a lubrication oil that keeps the fuel pump and other components running smoothly. Petrol, acting as a solvent when mixed with diesel, has the opposite effect.

Adding petrol to a diesel engine increases friction between parts, causing damage to the fuel lines and pump. If you drive away or even start the car with petrol in the mix, you could cause expensive damage to the engine.

READ MORE: How to improve your fuel economy

What happens when you put diesel in a petrol engine?

Diesel pump nozzles tend to be larger than most petrol fuel necks, so misfuelling in a petrol car doesn’t happen all that often.

Luckily, putting diesel in a petrol engine isn’t as bad as the other way around. Because diesel needs to be compressed before it’ll ignite, chances are you won’t even be able to start the engine.


Man on phone next to broken down car

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

First of all, and this is most important: Do not start your engine. Don’t even put the key in the ignition.

If you’ve realised your mistake before starting the engine, here’s what you do:

  • Tell the petrol station what’s happened.

  • Put the car in neutral.

  • Have someone help push your car to a safe place.

  • Call your insurer as soon as you can.

  • If you have breakdown cover, give them a call – they should be able to drain, flush and refuel your car.

If you aren’t so lucky and you drive off with the wrong fuel, you’ll soon realise what’s happened when the car grinds to a halt.

READ MORE: What to do if you break down - a step-by-step guide

Breakdown and insurance – are you covered?

Most standard breakdown cover policies will take you to the nearest garage or to your home. But draining the tank might come at an extra cost.

Some breakdown providers offer a drainage service as an add-on to their cover, so it’s worth checking beforehand. You can also compare garages that offer misfuelling services, though their prices may vary by a wide margin.

Whether or not you’re covered under your insurance is a trickier matter. Some insurers may include misfuelling cover as standard, but this isn’t the norm.

You might be able to claim for a drain-and-refuel under the accidental damage part of your policy. However, any resulting damage to the engine may not be covered.

In any case, it’s best to check the small print of your policy to make sure.

READ MORE: Warning signs that your car needs a service

Putting the wrong fuel in the car

How to avoid putting the wrong fuel in your car

The obvious answer here is to be attentive while filling up, but that’s sometimes easier said than done.

An alternative way to prevent this from happening is by fitting a diesel fuel cap to your fuel neck. This cap stops petrol nozzles from fitting into fuel tanks they’re not meant for.

These caps are designed to fit into specific makes and models, so be careful you choose the right one. Depending on your model, they tend to cost between £15 and £30.

READ MORE: What to do when your car won't start

First published 14 July 2016


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