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Topped up with the wrong fuel?

Date: Thu 22nd February 2018   |   Author: L Blake

It’s a simple mistake affecting 150,000 motorists a year

Roughly every three minutes in the UK, motorists put the wrong fuel in their car. That’s approximately 150,000 motorists a year. A lack of concentration, being in a rush or even filling your tank tired or hungry can cause this expensive mistake. In this blog, we explain what to do if you accidentally put the wrong fuel in your car.

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

If you’ve put the wrong fuel in your car how you deal with it depends whether the engine is started or not.

Don’t start the car...

If you haven’t started the engine and you’re still at the pump do not start your car. It should also go without saying that you shouldn’t put any more of the wrong fuel in. (There’s no point putting the correct fuel at this stage either as it will just go to waste and it won’t help your car now.) By not starting the car you are limiting the damage that the wrong fuel has caused for your vehicle.

Without putting the key in the ignition you should alert the petrol station staff so that you can move your car out of the way to a safe place. To do this, ensure the car is in neutral with the handbrake off. You will need to steer the car whilst someone else pushes it for you. You’ll then need to arrange for your car to be recovered so that it can be drained by a mechanic and assessed for damage. If you’re a member of the AA or RAC, their engineers sometimes carry equipment where they can drain fuel at the roadside.

If you’ve already started the car...

Unfortunately, if you’ve already started your car the damage will be worse. If you’ve managed to drive your car away from the garage with the wrong fuel you should stop the engine immediately and push your car to a safe place. The longer you leave the car running the more damage it will likely do to your car.

Your car will obviously need recovering and a mechanic will then be able to drain your fuel tank and check if your vehicle has any further damage caused by using the wrong fuel.

In both instances, you should also contact your insurance provider at the earliest possible opportunity.

What happens when you put petrol in a diesel car?

In diesel cars, adding diesel not only powers the car, the diesel also acts as a lubrication that keeps the components in the car running smoothly. However, mixing petrol with diesel has the opposite effect. Accidentally putting petrol into a diesel engine causes friction between parts, resulting in damage to the fuel lines and pump. 

Once you turn on the ignition you’ll circulate petrol throughout the entire fuel system and contaminate a range of components. The damage to your car can be vast and repairs can be extremely costly. It may even mean you have to replace the entire fuel system and you could still experience issues down the line. It’s likely that the engine won’t start and the car will be damaged straight away.

What happens when you put diesel in a petrol car?

It is less likely that you’ll accidentally put the wrong fuel in a petrol car, as most diesel nozzles won’t fit into a petrol car. However, if you do accidentally manage to put diesel into a petrol car and start the engine this will coat the spark plugs and fuel system with the wrong kind of fuel, which is never good. You’ll likely notice some of the issues below:

  • The engine won’t start.
  • The vehicle will misfire.
  • The engine will start smoking.
  • The engine will have a reduction in power - potentially a serious reduction.

Although it’s not desirable, putting diesel in a petrol car is less serious than vice versa and the damage is less severe. There will obviously be some repair costs to pay and an awkward call-out to recover your vehicle! The scale of the damage will depend on how long - or if at all - you were driving before you noticed your mistake. As soon as you notice the issue, stop the car and follow our advice above.

How to avoid putting the wrong fuel in your car

If you switch from a petrol to a diesel vehicle, often it can be hard remembering which fuel you need when filling up. To make remembering easier, you may find it helpful to leave reminder notes in your car. As well as putting your mobile away to avoid distractions. Some manufacturers apply a sticker on or by the fuel filler cap to remind you but you could always add your own.

We hope you found this blog post useful in understanding what to do if you accidentally put the wrong fuel in your car. There are plenty more posts on AutoProtect that can help you improve your driving knowledge and safety.