Using the wrong fuel nozzle can cost you several thousand dollars. For this reason, the engine of a diesel vehicle that has been filled with petrol by accident should not be started. The only exception is when the amount is very small, since petrol will mix with diesel. Petrol damages diesel engines because a diesel engine works under extremely high pressure, with viscous diesel also serving to lubricate the sensitive fuel-injection system. Petrol, on the other hand, is not an effective lubricant, and so the high-pressure pump and valves will wear out rapidly, with the added risk that fine metal fragments will travel through the system and cause additional damage.The result will be a loud 'hammering' from the engine, which is very likely to be ruined. If there is a filling station error, it is therefore cheaper to have the vehicle towed away and professionally cleaned. Pumping out the wrong fuel and cleaning the tank and all the pipes will only cost a few hundred dollars at most.