Petrol in a Diesel Car: Quick Fixes and Long-Term Solutions

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Filling up a petrol car with diesel is a common mistake that can happen to anyone. This mistake can lead to serious consequences for both the car and the driver. Diesel and petrol have different properties, and using the wrong fuel can cause severe damage to the engine, fuel system, and other components of the car. In this article, we will discuss what happens when you put diesel in a petrol car, the effects of mixing fuels, and the remedies to fix the problem.

What Happens When You Put Diesel in a Petrol Car?

The first thing that happens when you put diesel in a petrol car is that the engine will not start. Diesel fuel is thicker than petrol, and it cannot burn in a petrol engine. Diesel fuel will clog the fuel system and prevent the petrol from flowing to the engine. If the car does start, it will run roughly and produce black smoke from the exhaust pipe. This is because diesel fuel does not vaporise like petrol, and it will not burn completely in a petrol engine.

Effects of Mixing Diesel and Petrol

Mixing diesel and petrol can have severe effects on the car’s engine and fuel system. Diesel fuel is more viscous and has a higher cetane rating than petrol. This means that diesel fuel burns slower than petrol, and it requires higher compression to ignite. When diesel fuel is mixed with petrol, it reduces the octane rating of the fuel, making it less explosive. This can cause engine knocking and damage to the pistons, valves, and cylinder head.

Diesel fuel can also damage the fuel system components such as the fuel pump, fuel injectors, and fuel filter. Diesel fuel has a higher lubricity than petrol, and it can damage the rubber seals and gaskets in the fuel system. Diesel fuel can also clog the fuel filter and cause a reduction in the fuel flow rate. This can lead to a loss of power and engine damage.

Remedies to Fix the Problem

If you have accidentally filled your petrol car with diesel fuel, it is important to take immediate action. Here are some remedies to fix the problem:

  1. Do Not Start the Engine: If you have not started the engine, do not try to start it. This will prevent the fuel from circulating in the fuel system.
  1. Drain the Fuel Tank: The first step is to drain the fuel tank completely. This will remove all the diesel fuel from the fuel system. You can do this by siphoning the fuel out of the tank or by using a fuel pump.
  1. Replace the Fuel Filter: Diesel fuel can clog the fuel filter, and it’s essential to replace it with a new one.
  1. Flush the Fuel System: After draining the fuel tank and replacing the fuel filter, you need to flush the fuel system. This can be done by adding a petrol cleaner to the fuel tank and running the engine for a few minutes.
  1. Check the Engine Oil: Diesel fuel can contaminate the engine oil, and it is important to check the oil level and quality. If the oil is contaminated, it needs to be changed.
  1. Seek Professional Help: If you are not confident in fixing the problem yourself, seek professional help. A mechanic can diagnose the problem and fix it properly.


Filling up a petrol car with diesel fuel can lead to serious consequences. It’s important to take immediate action if you have made this mistake. Diesel fuel can damage the engine, fuel system, and other components of the car. You should also seek professional help if you are not confident in fixing the problem yourself. Remember, prevention is always better than cure, so be careful and double-check before filling up your car with fuel.

If you put petrol in a diesel car by mistake, don’t panic! Contact Fuel Fixer, a professional company that specialises in misfuelling solutions. Our team of experts can provide fast and efficient assistance to get you back on the road in no time. We offer a nationwide service, and our technicians use state-of-the-art equipment to drain the contaminated fuel, flush the system, and get your engine running smoothly again. Give us a call to get immediate assistance for wrong fuel cleanup.

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