What Happens if You Misfuel Your Car?

While some modern cars are fitted with preventative fuel caps to try and stop owners from inadvertently using the wrong fuel, putting petrol into a diesel vehicle or vice versa can be disastrous.

These incidents can cost anything from around £200 for a simple drainage service, to thousands if you have driven with the incorrect fuel in your vehicle, which can cause serious damage to the engine.

Around 150,000 people make this mistake every year, often due to a lack of attention, rushing to refuel during a busy day, or using a petrol station without realising the pumps are arranged differently.

Porsche OEM parts specialists Design911 looks at what happens if you put the incorrect fuel in your vehicle, the damage to your car it can cause, and how to react if you realise you’ve used the wrong pump.

Why Is Misfuelling a Serious Problem?

It may seem that petrol and diesel are not remarkably different, but there is a good reason fuel caps come with labelling that indicates which types of fuel are compatible with your car engine.

When you put the wrong fuel into your fuel tank, it starts mixing with the alternative fuel type. Turning the key in the ignition means that the mixture begins circulating throughout the car engine system.

The level of damage depends on the vehicle, how far you have driven, and the types of fuel used, but it can affect almost every part of the engine, including:

• Pipes
• Fuel tank
• Filters
• Injectors

Petrol in a diesel engine acts like a solvent, which stops the diesel from lubricating the fuel pump, increasing the friction in the engine. If the fuel pump keeps running, the metal surfaces grind together and disintegrate generating a swarf, which means tiny metal particles start circulating the engine system.

High-pressure injectors then force the fuel through the cylinders, and if the swarf gets this far, it will block the holes in the cylinders, meaning you may require a completely new injector system.

Putting petrol in a diesel car causes more damage, mainly because it is often possible to start the engine and drive away. In contrast, a petrol vehicle may not start at all if it has been misfuelled, bringing the issue to your attention.

Diesel pumps have slightly bigger nozzles, so it’s less likely you’ll put diesel into a petrol car, whereas a slimmer petrol nozzle can fit inside a diesel filler cap.

What Does it Cost to Fix a Car After Misfuelling?

Repair costs depend on the vehicle's age, design and size, how much of the wrong fuel you have pumped into the tank, and whether you have noticed the error, or have driven away.

Draining fuel from an easily accessible fuel tank can be straightforward, but if the vehicle has a tank and piping underneath the car, the process can be more complex and will need to be completed in a garage with a car lift.

Other cost factors include the vehicle's location since you won’t be able to drive, so if your car needs to be booked into a garage for repair you will need to arrange for a tow truck.

Fuel drains vary with the type of fuel, as your tank could contain a mixture of petrol and diesel along with other substances such as AdBlue and water which may have reached the fuel lines.

If the misfuel has caused damage to other parts of the engine, the repair costs will depend on whether those parts can be repaired or need replacing. Replacing an entire engine can cost several thousand pounds especially for high-performance premium vehicles or commercial vans with larger components.

What Should I Do if I Misfuel My Vehicle?

The first thing to do is turn off the engine and remove the key from the ignition straight away. Never try to start a car that has been misfuelled, even if it appears to be working or you believe there is only a small amount of the wrong fuel in the tank.

Removing the key is important because even if you don't start the engine, inserting your key activates your fuel pump while your dashboard light illuminates. Diesel vehicles operate this way to prime the engine and begin circulating fuel before you start the car, so if you leave the key inserted, petrol could be sucked up the fuel lines.

Put the car into neutral or park, depending on whether you drive a manual or automatic, and let the staff at the petrol station know, or ask for assistance to push the car to a safe space, parking refuge or layby where it won’t cause an obstruction.

If you have already started the car or driven any distance, turn off the engine immediately, or pull off the road at the earliest opportunity.

The next step is to arrange a towing service to collect your car and take it to your mechanic. They will be able to assess the damage caused to the vehicle, flush the tank and drain the fuel pipes, and let you know whether any parts need replacing before the car is safe to drive.

You may find that, if you have realised you have misfuelled at the forecourt, the repair work can sometimes be carried out on-site without needing to tow your vehicle - but if you've driven away with the wrong fuel in your tank this will not be the case.

How to Avoid Misfuelling

Some modern vehicles are more difficult to misfuel and feature devices fitted to the cap, where only the correct fuel pump nozzle will fit into your car. Most vehicles also have stickers or labels inside the fuel cap showing the fuel types you can use.

Petrol vehicles can normally use either E5 or E10 petrol, and all cars built from 2011 onward are compatible. Still, some older vehicles may only be able to use E5, usually the super-grade petrol alternative.

If you have any doubts about which fuel to use in your vehicle, it is well worth checking the handbook before you fill up to ensure you don’t mistakenly use the wrong pump.

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Media Contact:

Tom Harper-Ward
Design911

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Source Company - Design911