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 that 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.

Step-by-step guide

When you realise what you’ve done, stay calm and follow these next steps:

  • Put your car in neutral.
  • Let the petrol station attendant know what’s happened so you have immediate support.  
  • Ask for help to push your car to a parking spot nearby, so you’re not blocking a fuelling spot.
  • Ring your own or a local breakdown provider, or search for one of the national ‘wrong-fuel’  service companies.  They will send someone to rescue you, either to drain, flush and refuel your engine for you on site,  or get you towed to a local garage to do this for you.  
  • Once your engine has been cleaned, and you have the right fuel, you can be on your way.

If you’ve not realised what you’ve done on the forecourt and have driven off, your car will soon let you know, by breaking down. You will then need to call your Breakdown service or any recovery service, to get you to a local garage and have the wrong fuel drained away and the engine repaired, if required.

Will I have to pay to put it right?

Most breakdown cover  - and this includes Rias Breakdown cover - doesn’t include draining your engine or removing any contaminated fuel or other fluids. Rias Breakdown service does provide cover for towing  you to the nearest garage to get the wrong fuel flushed out for you. The cost of draining and flushing varies, a standard price could be between £150 and £200.  

 If you’ve started your car and attempted to drive off, fixing the damage to your engine isn’t going to be cheap - it could cost anything from £200 up to £3,000 or more,  depending on the car and how far you have driven.  The good news is that Rias car insurance customers are covered for the cost of any repairs, or even a replacement engine, resulting from mis-fuelling, but not for the initial draining and  flushing out of the wrong fuel.  

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 that 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, and 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 prevent it happening again?

Most mis-fuelling happens because people are rushing, distracted or hungry; 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, and if you have a diesel car you might want to consider buying a cap that goes on your filler neck to prevent petrol nozzles from fitting into it - but there is no equivalent for petrol cars.