The term “misfuelling” is used to refer to the situation when the wrong fuel is put into a vehicle. According to the AA, over 150,000 drivers fill up their vehicle with the wrong fuel each year, with the majority driving a car they are not used to, such as a courtesy car or hire vehicle. Misfuelling can be a costly business and so make sure that you are using the right fuel is very important.

Filling up your car with the wrong fuel will result in your car breaking down, and you may need to pay thousands to replace some parts in your car. Therefore, you should always try to pay attention and double check you know which fuel to use in your vehicle every time you fill up. To help you remember, you can buy caps for your diesel to help you prevent putting petrol in from most car parts shops.

There is not a specific fuel cap you can buy to prevent you putting diesel in a petrol tank because it is actually quite tricky to put diesel into a petrol car. This is because the standard diesel nozzle is bigger than the filler neck of modern petrol cars. Therefore it is more common for petrol to be put into a diesel car than the other way around.

What to do if you’ve mis-fuelled:

If you realise you have filled the car up with the wrong fuel, do not turn on your ignition or start the engine. It is imperative to not turn the engine on because as you turn on the vehicle, the fuel will circulate in the tank and cause damage to your engine. Therefore, if you realise you have misfuelled, you should put your car into neutral and push your car to a safe location or alert the petrol station staff, and they will be able to assist you further.

You should then find out if your insurance policy covers misfuelling as some will provide you with a misfuelling service at a reduced if not free cost, although this will count as a claim against your insurance. If your insurance doesn’t cover misfuelling ask the petrol station if they have any contacts, if not a simple google search will bring up the closest people near you who can deal with misfuelling although some larger companies may provide you with a service.

Obviously, some people fill up their car with the wrong fuel without realising until they are driving down the road and the performance of the car is affected if it moves at all. As soon as you realise you have filled up your car with the wrong fuel, stop the car safely, turn off your engine and call your insurance or a misfueller you have a contact for, for advice on what to do.

Petrol in a diesel car

Petrol fuel in a diesel acts as a solvent, reducing lubrication processes in the engine. Because of this, putting petrol in a diesel can cause considerable damage to the fuel pump and other parts in the engine. A small amount of petrol in a diesel car should not do too much damage to the engine as long as it is less than 5 litres of petrol. In this scenario, you should top up with diesel and continue as usual unless advised not to by the car manufacturer or insurance provider.

More than 5 litres of petrol in a diesel tank will need professional assistance. You will either need your car drained and the parts cleaned, or you may need parts replaced if you have driven with the wrong fuel in your car.

If you end up needing parts replaced it can cost thousands to repair. However, if you do not turn on the engine, then you will only need the tank drained and refilled with the correct fuel which will cost hundreds and could save you having to claim on your insurance.

Diesel in a petrol car

As previously mentioned, putting diesel in a petrol tank is less common than putting petrol in a diesel because the diesel nozzle at fuel stations is bigger than the filler neck for petrol cars.

However, we all have our moments, and this situation can still happen. If more than 5 litres of diesel is added to a petrol car, the diesel will not ignite the spark plug like petrol would, and the car will not move. The car will then need to be drained and the fuel replaced.

If less than 5 litres of diesel is added to a petrol car, dilute it with petrol and the car should be functional although the exhaust will be smokey and it may feel different to drive. Diesel in a petrol tank is less damaging than petrol in a diesel tank.

Claiming on your insurance

If you put the wrong fuel in your tank and then start the engine, you will probably have to take your car to a garage. If you are lucky, the garage will only need to drain the tank, clean the hoses and remove the fuel from the pumps. However, sometimes the wrong fuel will cause huge damage to your engine meaning parts of your engine, or your whole engine will need to be replaced. This sort of repair can cost thousands of pounds.

Some car insurance providers will cover the costs of a new engine and repairs when the wrong fuel has been put into a vehicle. They will usually cover it under accidental damage to the vehicle. However, as more diesel cars come into the market and the problem becomes more common, some insurers are deciding not to cover the repairs for wrong fuel in their policies. Therefore you should always read your car insurance policy wording to see if misfuelling is covered.


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