Unleaded petrol causes damage to a diesel engine. According to the Automobile Association, at least 150,000 drivers in the United Kingdom pump the wrong fuel into their vehicles annually, an occurrence known as "misfuelling."
Drivers often misfuel due to a recent conversion from petrol to diesel vehicles. This costly mistake is usually committed because, coupled with a lack of a misfuel device, the unleaded nozzle conveniently fits into the filler of a diesel engine. When a diesel engine is filled with unleaded petrol, the petrol strips the engine's protective lubrication, which causes serious damage to the high pressure engine pump. At times, engine repairs are not sufficient and the entire engine fuel system requires changing.