Tips and Advice

Misfuelling: what to do if you put petrol in your diesel car

It's a more common mistake than you think, but what do you need to do if you put petrol in your diesel car?

Putting the wrong fuel in your car at the pump – called misfuelling – is a terrible shock but not as rare as you might think. Every year in the UK, around 150,000 drivers misfuel, often when they’ve recently switched from a petrol to a diesel car.

Putting petrol into a diesel tank is far more common, because a forecourt diesel pump delivery nozzle is wider than a petrol car's filler neck will accept. This means it's very easy to accidentally put petrol in a diesel car, but you have to be pretty determined to do it the other way round.

If you do misfuel your car, don't panic – here's our guide to what you should do.

Petrol or diesel: which is best for you?

What should I do if I misfuel my car?

Putting petrol in a diesel car is not necessarily the end of the world if you were fortunate enough to realise your mistake quickly, and haven't tried to start your engine.

If you’re still at the filling station, whatever you do, don’t turn the key any further than you need for the steering wheel to unlock. Turning it further will cause the fuel pump to send contaminated or incorrect fuel into the engine, multiplying your problems. Instead, find help to push the vehicle clear of the pumps to a safe place.

If you have breakdown cover, give your provider a call. They may be able to fix the problem where you misfuelled it, rather than taking your car to a garage. It's worth telling your insurer what’s happened, too, as keeping them informed could make it easier to claim for repairs later, if they’re required.

It’s vital that the entire fuel system is drained of the wrong fuel. Depending on the amount of fuel in the tank, some breakdown companies such as the AA and RAC can do this at the roadside. Otherwise, your car will have to be towed to a garage that can do the job.

If it’s a diesel car, after the tank, fuel lines and filter have been been drained, the tank will need to be refilled and the system primed to remove any air that could prevent the engine running properly.

I misfuelled my car and started the engine. What do I do now?

The above assumes you realised your mistake immediately. If, however, you filled up, started the engine and drove away, only to come to a spluttering halt, you’re in more serious trouble. Now, rather than just being in the tank, the fuel is deep in the car’s engine and fuel system where it can cause problems.

Petrol that has entered a diesel engine can cause major issues. You'll need to call your breakdown recovery provider and have the car towed to a garage for examination and repair. You may be fortunate, but it’s not unusual for a repair bill to run well into four figures. Check with your insurer if you’re covered. If the car isn’t worth very much, it may write the vehicle off.

If you have only pumped a very small amount of petrol into your diesel car, you may not notice any difference to how it runs. However, it's still a good idea to have the system properly drained and the fuel filter changed, as petrol is a solvent and can cause damage to diesel pump components. Petrol can also potentially damage a diesel engine during the combustion cycle because it’s more volatile than diesel.

How to avoid misfuelling in the first place

The best way to avoid misfuelling is to put a sticker on the filler cover reminding you what fuel is required. There are also devices you can buy that prevent misfuelling. Also, consciously remind yourself what fuel is required, rather than fill up on autopilot.

Meanwhile, carmakers such as Ford provide a so-called ‘Easy Fuel’ system that prevents you putting the wrong fuel in your car.

If you don't want to worry about refuelling, check out our guides to electric car charging stations and the best electric cars.

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