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Wrong fuel in your car? Here's what to do

A fuel pump nozzle.

Putting the wrong fuel in your car is a common mistake to make. According to the RAC, nearly 150,000 motorists fill their tank with the wrong fuel every year. That means someone makes the mistake of misfuelling their vehicle every three minutes.

If you've been caught out, don't worry. Just follow our guide to avoid any lasting damage to your car.

Don't start the car!

While it's more common to put petrol in a diesel car (with this happening to 95% of misfuelling incidents), it's just as easy to put diesel in a petrol car.

Whatever the mistake, the first step is always the same: don't start the engine. By not turning the key, you will avoid circulating the mixed fuels around the engine and causing more, potentially costly, damage to your car.

If you've already driven off, try to stop as soon as possible in a safe place, move away from your car and call for assistance.

What to do next

If you've realised your mistake and haven't switched your engine on, inform the service station attendant of what's happened, and then call either your car insurance company or breakdown cover if misfuelling is covered under your policy. Follow the instructions they give you as failing to do so could invalidate your cover.

If you aren't covered for misfuelling or don't have the relevant numbers on you, the service station attendant might be able to provide you with a number for a local assistance company.

Once help has arrived, they'll drain the fuel and flush your engine. Some companies might even replace your contaminated fuel with clean fuel.

What happens when you misfuel?

Diesel and petrol work differently, as do the engines designed for each of these fuels. So, the damage that happens to your car will depend on the engine and the fuel it's supposed to have.

When you put petrol in a diesel car

Putting petrol in a diesel car is the most common type of misfuelling as petrol nozzles easily fit into modern diesel cars. However, it's also the most serious type of misfuelling.

If it's not dealt with straight away, putting petrol in your diesel car will damage your fuel pump. Diesel helps the fuel pump do its job by acting as a lubricant, but when it's mixed with petrol it has the opposite effect and acts like a solvent. The loss of lubrication will cause the metal parts to come into contact and rub together. This means it will do more damage the more it's pumped through your fuel system. This type of misfuelling can even result in needing a new engine.

HDi or common rail diesel engines can suffer particularly bad damage as a result of misfuelling, which could mean you need to look at new fuel pumps, injectors, pipes, filters and fuel tank.

When you put diesel in a petrol car

As the petrol filler necks on most cars are much smaller than the diesel nozzle, this type of misfuelling is not as common. Whilst putting diesel in a petrol car doesn't have the potential to cause as much damage as putting petrol in a diesel car, it can still cause serious damage. This type of misfuelling is particularly harmful to direct injection (GDI) petrol engines.

How to prevent misfuelling

Driving a new car or driving several different cars can cause confusion at the petrol pumps. To save the cost and hassle of misfuelling, here are some top tips:

  • Don't just rely on the colour of the hose or nozzle. Be sure to check the fuel pump indicator and the pump trigger.
  • The fuel pump is not a good time to get distracted, especially if you have a new car, so concentrate.
  • If you're still getting used to a new car, or even a hire car, it can be useful to leave little reminders around.
  • If you drive a diesel car and misfuelling is a concern, there is a device you can buy that inserts into your filler neck so a narrower petrol nozzle can't be inserted.
  • While misfuelling is a common mistake, not all car insurance or breakdown policies cover you for this so check your policy documents to see if you're covered. If you're not covered, you can buy stand-alone policies especially for misfuelling vehicles.

All information is correct at time of publication. Hastings Direct cannot be held responsible for any misinformation displayed.

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