Filling your vehicle with the wrong type of fuel, whilst upsetting, is more common than you might think. According to the RAC, there are about 150,000 incidents of “misfuelling” in the UK every year.

Digging deeper into the above, Independent Advisor Car Insurance uncovered that in the UK, there are an estimated 80,520 searches on average for variations of "what to do if you put the wrong fuel in your car?" a year.

Hundreds of thousands are expected to make lengthy journeys across the country this Bank Holiday, with traffic induced stress leading to making mistakes when fuelling.

With this in mind, Connor Campbell at Independent Advisor Car Insurance shares their expertise on what to do if you put the wrong fuel in your car

What to do after putting the wrong fuel in your car?

Realising you have misfuelled before you start the ignition is the best case scenario, as keeping the engine turned off will limit the damage done to your vehicle. What to do next is vital, according to Connor Campbell, expert at Independent Advisor Car Insurance:

“Leave the ignition switched off, don’t put your key in the ignition or turn it to the initial ‘accessory’ position to turn the radio on or wind-up your windows. Next, tell a member of staff at the service station. Put the car in neutral and push it to a safe place as directed by service station staff. You can then apply the handbrake without starting your engine. Call for help - this might be your insurer if misfuelling is included in your policy, your breakdown provider, or a specialist company that can come out and drain your tank.”

What if I’ve already started the car?

If you have already turned on the ignition, don’t panic. Taking the right action can limit the damage done to your vehicle. According to Connor Campbell:

Turn off the engine immediately if it’s safe to do so – if not, find a safe spot and stop. If you can, put the vehicle in neutral and push it to a safe place and then call for help, either from your insurer, a breakdown company or a wrong fuel specialist.”

How to tell if you’ve put the wrong fuel in your car

There are some immediate and common signs you might experience if you’ve misfuelled your car.

The signs to look out for if you have put petrol in a diesel car:

  • The engine not starting or stopping abruptly
  • Loud knocking/banging when you accelerate
  • Excess smoke coming from the exhaust
  • Loss of power when accelerating
  • The engine warning light illuminating

The signs to look out for if you have put diesel in a petrol car:

  • The engine not starting
  • Smoke coming from the exhaust
  • The engine misfiring

What kind of damage can putting the wrong fuel in your car cause?

On average, the cost of having fuel drained from your vehicle could range from £120 to £1,000 in best case scenarios. However, depending on how long you have driven with the wrong fuel, where your fuel tank is located or how much you put in, it can add up to be a lot more as the car will need to be repaired.

Putting petrol in a diesel car

Putting petrol into a diesel car is the most common form of misfuelling as the smaller petrol nozzles easily fit into diesel cars.

Misfuelling this way causes the most damage if you turn the ignition key. Illuminating the dashboard lights could mean your fuel pump kicks into life, but instead of priming the engine with diesel before it starts, your car will be sucking petrol up the fuel lines. This means they’ll need draining and flushing as well as the fuel tank.

If you actually start the engine, things will be even worse. Diesel acts as a lubricating oil, making sure the engine parts run smoothly and helping to minimise wear and tear. However, when petrol is added to diesel, the resulting mixture behaves like a solvent that dissolves the lubricant. This will increase the friction between engine parts, which can cause severe damage.

Putting diesel in a petrol car

Drivers are less likely to accidentally put diesel in a petrol car as the diesel fuel pump nozzle is much larger than a petrol nozzle. However, while it’s a more difficult mistake to make, putting diesel in a petrol vehicle is likely to be a much bigger problem than the reverse scenario.

The lubricating properties of diesel mean the fuel will coat the spark plugs and fuel system which can often lead to misfiring, smoke, and the engine either failing to start or cutting out. If you realise you have misfuelled before putting the key in the ignition, the fuel tank will need to be drained and flushed, and can then be filled with petrol as normal.

However, if you start the engine, soot will quickly build up on the spark plugs, causing the fuel injectors to become clogged and your engine to lose power. In this situation, as well as the fuel tank needing to be drained and flushed, the fuel lines, spark plugs, fuel filter and injectors could also need inspecting. The system will need to be properly cleaned, but after that you should be able to fill with petrol as normal.

Putting E10 petrol in a non-compatible car

E10 petrol became the standard grade of petrol in England, Scotland and Wales in September 2021 and in Northern Ireland in November 2022. E10 petrol is blended with up to 10% renewable ethanol, making it a more environmentally-friendly fuel.

However, E10 isn’t compatible with a number of older cars. You can check if your vehicle can run on E10 online.

If you put E10 in a non-compatible car, it may still run, but if you keep using E10 some parts may become damaged over time. There’s no need to drain the tank if you fill up with E10 – just put the right fuel in as soon as possible to dilute it in your car’s system.

Visit Independent Advisor Car Insurance for more expert insights.