Misfuelling – what to do if you use the wrong fuel

Misfuelling is a very common occurrence in the UK. It can happen to anyone, all it takes is a little distraction at the pumps and you’ve caused a big problem for your engine. 

You’re even less familiar with your hire car, so you’ll have to take extra care when it comes to filling up. 

But what actually happens to your vehicle if you’ve used the wrong fuel, and what do you need to do if it happens to you? 

Putting diesel in a petrol engine

Putting diesel in a petrol engine is much less damaging than the other way around. However, it’s less common thanks to the different nozzle sizes for the two types of fuel. Diesel pump nozzles are typically bigger than an ordinary petrol fuel neck, so it’s harder to use the wrong one on the forecourt. 

If you’ve managed to get diesel into a petrol engine, it’s likely you won’t even be able to start the vehicle. Before it can ignite, diesel needs to be compressed and your petrol engine isn’t up to the task. 

woman misfuelling her car at the petrol station

Putting petrol in a diesel engine 

If you’ve accidentally put petrol in a diesel engine, you must not start your vehicle. Don’t even put your key in the ignition; you don’t want the two fuels to start mixing in the engine. If you start the vehicle and drive away, you’ll be doing very expensive damage. 

Diesel doesn’t just power the engine, it acts as a lubricating oil that helps keep all the components of an engine running. When mixed with petrol, it has the opposite effect. There will be more friction between the parts of your car causing big problems for the engine. 

You’ve used the wrong fuel, but what next? 

If you’ve realised you’ve used the wrong fuel before you’ve started the engine, great! You’ve avoided a breakdown somewhere between the station and your next destination. 

There are some simple steps you can follow to get the problem resolved: 

  • Tell the petrol station – this won’t be the first time they’ve seen this happen
  • Put the vehicle into neutral 
  • Grab a volunteer to help you push the vehicle to a safe place
  • Call your insurer – you’ll have all these details from us when you hired the vehicle 
  • Contact your breakdown service – all our vehicles have roadside recover and home start cover. Most policies offer drainage service as an add-on, but typically draining the tank comes as an extra cost

If you’ve misfuelled and haven’t realised before driving away, you won’t get very far before coming to a stop. If that’s the case, you’ll need to handle the situation like you would for any other breakdown. 

man misfuelling his car at the petrol station

How to prevent misfuelling 

To help stop yourself from misfuelling, make sure you’re paying attention at the pumps. We know it’s easy to get distracted and to fill up on autopilot, but a few moments of concentration can save you a big bill. 

Misfuelling is most common when the vehicle is new to you, that’s why you need to pay close attention when filling up your hire car. If you own the vehicle, you could invest in a reminder sticker to put on the fuel cap as a helpful reminder every time you fill up. 

Or, to avoid the really costly damage to a diesel engine, you can purchase a fuel cap that prevents petrol nozzles from fitting inside your tank. These vary in price for different models but don’t typically cost more than £30 – much more affordable than a massive repair bill. 

Looking to buy a used car, van or truck? Check out our great range of vehicles for sale, complete with full service history. 

Browse vehicles for sale