misfuelling

Misfuelling occurs when a person incorrectly fills a vehicle's fuel tank with the wrong type of fuel. The most common scenario is putting diesel into a petrol (gasoline) engine or petrol into a diesel engine. This mistake can happen due to the similarity in appearance of the fuel pumps and nozzle sizes, especially in some regions.

The consequences of misfuelling depend on the type of engine and the fuel mixture. Petrol in a diesel engine can damage the fuel pump and injectors because diesel fuel acts as a lubricant, while petrol has no lubricating properties. A diesel engine running on petrol may start but will likely run poorly, misfire, and eventually stall. Conversely, diesel in a petrol engine can cause significant damage to the engine's internal components and the catalytic converter. Petrol engines rely on spark ignition, and diesel fuel, which ignites under compression, will not combust properly in this system, potentially leading to knocking, stalling, and subsequent engine damage.

If misfuelling is discovered before the engine is started, the best course of action is to not start the vehicle and have the fuel tank drained and flushed. If the engine has been run, it is crucial to stop the vehicle as soon as safely possible and seek professional assistance. Attempting to drive the vehicle further can exacerbate the damage. Many modern vehicles have features to prevent misfuelling, such as smaller diameter diesel nozzles that won't fit into the wider opening of a petrol filler cap, but these are not universally present.