Putting diesel in petrol car is a common mishap that can cause significant engine problems. While generally less catastrophic than putting petrol in a diesel car, it is a serious issue that requires immediate attention to avoid costly repairs.

Petrol engines are designed to ignite a fine mist of fuel and air with a spark plug. Diesel fuel is much thicker and oilier than petrol and does not ignite in the same way.

When diesel is introduced into a petrol engine, it will:

Clog the fuel system: The thicker consistency of diesel can block fuel filters and injectors.

Coat the spark plugs: The oily nature of diesel will foul the spark plugs, preventing them from creating the necessary spark to ignite the fuel.

Disrupt combustion: Because diesel doesn't ignite easily with a spark, it will lead to misfires and prevent the engine from running smoothly, if at all.

Essentially, the diesel will act as a contaminant, preventing the petrol engine from operating as it should

If you have mistakenly filled your petrol car with diesel and have started the engine, you will likely notice these symptoms quite quickly:

Difficulty starting the engine: The engine will struggle to turn over as the spark plugs fail to ignite the contaminated fuel.

Misfiring and juddering: If the engine does start, it will run erratically and lack power.

Excessive smoke from the exhaust: Unburnt diesel fuel will be expelled through the exhaust, creating a noticeable, often white or grey, smoke.

The engine cutting out: The engine will likely stall and refuse to restart.

The engine warning light will illuminate on your dashboard.

If you realise your mistake at the fuel station, the most critical action you can take is to not start the car. Do not even turn the key to the 'on' position, as this can prime the fuel pump and circulate the diesel into the engine.

Here’s what you should do instead:

Leave the engine off.

Inform the petrol station staff of the situation.

Put the car in neutral. With help, push the car to a safe parking spot.

Call our wrong fuel assistance. We have the equipment to safely drain the contaminated fuel from your tank and flush the system.

No matter if you are at the roadside, in a forecourt or at home, the Misfuelled Car Fixer team can come to you at any time and offer our expert fuel drain service.

To find out more, please contact us using our details below.