Wrong fuel: What to do if you put diesel in a petrol car or petrol in a diesel car

We have heard of stories where people accidently put the wrong fuel in a car. This problem is actually more common than one can imagine. In most modern cars, diesel engines have become a lot more silent and in many old cars, even the petrol engines make a loud noise. This at times might create confusion among the fuel pump employees. Most of the modern cars now have a label on the inner side of the fuel lid that shows whether the car uses petrol or diesel fuel. Even then, this mistake can happen. We had reported one such incident where a brand new Volvo XC90 that belongs to a Karnataka MLA got filled with diesel instead of petrol.

In the past, we have written about the consequences of putting the wrong fuel in a vehicle. Just imagine, you are in a hurry and you just hand over a Rs 500 currency note to the petrol pump employee and ask him to fill fuel. You forget to specify which fuel and late you realise that the employee had put the wrong fuel. In case of a petrol engine the engine would choke if it is filled with diesel. Similarly, most modern diesel cars are very sensitive and can easily damage the engine. If you realise the mistake soon, there are ways to save the engine and the car.

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Symptoms of diesel in a petrol car

Why can’t you put diesel in a petrol car? Well, diesel is much heavier and that makes it more oily than petrol. Initially, the fuel filter of the car would take the imact. It would clog up almost immediately as it is more heavier than the petrol. Once this happens, you would start noticing that the car is stalling a lot and is stuttering. After this the spark plugs would be impacted. Spark plugs will foul up with soot build up after the fuels get mixed. After this happens, the car would start emitting white smoke and ultimately lose all its power before coming to a standstill.

Symptoms of petrol in a diesel car

Diesel engines are way more harsher than petrol engines. Putting petrol in a diesel car is way more expensive than the above mentioned scenario. This is because diesel engines are equipped with technology such as the fuel injection pump that is dependent on the diesel’s lubrication properties to function. Even the rubber seals in the diesel engine cannot handle the cleaning properties of petrol. It is difficult to diagnose the wrong fuel issue in diesel cars. The car would emit black smoke because of the unburn fuel and would eventually come to a complete stop.

What to do if you’ve put in the wrong fuel?

If you realise that you have put wrong fuel in the car and you have not started the car yet, best thing is to disconnect the main fuel line for the engine to the tank. Get help from a mechanic for this. You have to access the fuel tank using a hose and get as much fuel as possible. Drain leftover fuel from the main fuel line. Once the fuel is completely drained the fuel from the tank, crank the engine couple of times by turning the key. By doing this, the leftover fuel in the tank would also drain out. After this, fill around 2 litres of correct fuel and crank the engine to clean the fuel lines and residue of the wrong fuel from the tank. Once you are sure that the fuel has completely drained out, connect the fuel line back and fill the car with correct fuel. If this happens in a petrol car, then the fuel filter has to be changed and the spark plugs have to be replaced. In diesel cars, do check the drain plug at the bottom of the filter and drain out any fuel remaining in the filter as well. Thereafter prime the vehicle using a manual diesel pump and start the car.

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