Back to Tips and Guides

What should you do if you put the wrong fuel in your car?

We all make mistakes occasionally, but when it involves putting petrol in your diesel car or vice versa, it can feel like a disaster. First and foremost, it’s important you don’t put the key in the ignition or switch on the engine if you can help it. Here’s what you need to do next...

Your step-by-step guide

When you realise what you’ve done, it’s important you don’t panic.

  1. Put your car in neutral.
  2. Go back inside and tell the petrol station attendant what’s happened.
  3. Ask someone to help you push your car to a parking spot nearby, so you’re not blocking a fuelling spot.
  4. If you have breakdown cover, ring the breakdown line and they’ll send someone to drain, flush and refuel your engine.
  5. Once your engine’s been cleaned, and you have the right fuel, you can be on your way.

If you’ve not realised what you’ve done and driven off, your car will soon let you know by breaking down. You should then ring your breakdown line, and they’ll drain, flush and refuel your engine as above.

Will I have to pay out to put it right?

Most breakdown cover doesn’t include draining your engine, so you may have to pay for this, unless you’ve already added it to your policy as an extra. If you’ve started your car and attempted to drive off, fixing the damage to your engine isn’t going to be cheap.

What does using the wrong fuel do?

If you add petrol to a diesel engine, it acts as a solvent. It mixes with the diesel present – even if it’s only a tiny amount – and increases friction, which can damage your pump and fuel lines. The more petrol that gets pumped through your engine, the more expensive it can be to put right, so don’t start your engine. In worst case scenarios, the damage can be so severe a completely new engine is needed.

The consequences of putting diesel in a petrol engine aren’t as bad because diesel won’t ignite without being compressed. This means that aside from your car not starting and your spark plugs getting clogged up, no real damage should be done to your car’s engine. It’s actually quite unusual to make the mistake of putting diesel in a petrol engine, as the nozzles of diesel pumps are larger, so don’t fit as well.

How can I try to stop it happening again?

Most misfuelling happens because people are rushing or distracted, so try to make sure you’re focused on the job at hand every time you go for fuel. You could leave reminder notes inside your car, or stuck to the fuel cap. If you have a diesel car, you might want to consider buying a cap that goes on your filler neck to stop petrol nozzles from fitting into it – but there’s no equivalent for petrol cars.