In a diesel engine air is compressed using high pressure and then diesel is injected into the  combustion chambers through fuel injector nozzles. The simultaneous meeting of hot pressurised air and diesel repeatedly is what keeps the engine running. When you pour petrol in a diesel engine, you end up damaging the fuel injection pump that keeps the mill running. Now as you know, petrol is very volatile and has a low ignition temperature. When petrol comes in contact with pressurised air, it will burn immediately destroying the lubrication of the engine. In most cases it will fail to start if the quantity of petrol is too high.



If you put diesel in a petrol engine, the fuel mixture will take time to burn. In most cases your diesel car will not start because diesel is viscous (thick) and is being subject to spark ignition instead of compression. If you do manage to start and drive the car, soon enough there will be engine misfiring, abrupt engine cuts and a trail of white smoke to deal with. The car will quit running and will not start again until you fix the problem. This will involve draining the tank, installing new fuel filters because the thick fuel will ruin the petrol injectors.



Don’t switch on your car : You will ruin your car since in the case of diesel engine which has more expensive parts, you stand to lose a lot. Switching on your car’s ignition will circulate this mix of petrol in diesel through your fuel system, causing further contamination to other components.


Disconnect the main fuel line from the engine to the tank. Use it the car’s fuel pump to drain the unsuitable fuel.


Drain the fuel tank: If you realised your mistake at the pump itself then try and drain the car immediately. Ask the petrol pump attendants to help since they see this happening more often.


In case of  a petrol car, once the car is drained out appropriately, crank up the engine. Crank the engine until it starts for no more than twenty or 30 seconds at a time. Wait for the last drops of contaminated fuel to be removed from the mixture for two-three minutes and then fill in petrol.


Exercise all precaution to see the vehicle does not catch fire




In both cases:


Call for a recovery vehicle or contact your dealer: Stop trying to make the car start and get professional help as soon as possible. In places where you are not equipped to deal with such a situation it is important that you exercise caution and get the vehicle towed to some place safe so as to not endangers lives or damage your vehicle further.