What to Do When You Put Petrol in a Diesel Engine: Expert Advice

Putting the wrong type of fuel in your car can be a costly mistake, both in terms of the hassle and the damage it can cause to your engine. If you’ve accidentally put petrol in a diesel engine, you might be worried about the consequences.

put petrol in a diesel engine

In this article, we’ll walk you through what to do if you’ve made this mistake and whether it will harm your engine.

What to do After Putting Petrol on a Diesel Car

Stop driving immediately if you’ve accidentally put petrol in a diesel engine. Do not start the engine or turn the key. Contact a professional mechanic to drain and replace the fuel tank with diesel. Running a petrol engine on diesel can cause engine, fuel system, and emission control system damage.

Don’t Start the Engine

If you realize you’ve put petrol in your diesel engine before starting the car, do not start the engine.

Starting the engine will circulate the petrol and can cause significant damage to the engine’s components. Instead, have your car towed to a repair shop or contact a fuel draining service. This is the safest and most efficient way to minimize damage to your engine.

Damages of Petrol to Diesel Engines

Filling petrol into a diesel vehicle can cause serious damage to the fuel injection system and the engine. This is because the diesel fuel pump operates on very fine tolerance at high pressures, lubricated by the diesel fuel.

  1. If you add petrol instead, there isn’t as much lubrication, which can cause wear on the engine internals.
  2. When petrol is added to the diesel fuel tank, the diesel fuel already present will act as a solvent and strip lubrication away from the engine components.
  3. It can increase wear and tear on fuel pumps, fuel injectors, and fuel system components.
  4. Additionally, petrol is more combustible than diesel and will ignite much sooner than diesel.
  5. It can cause damage to the engine and potentially cause a fire hazard

Symptoms of Putting Petrol on Diesel Engines

Here are some of the symptoms of putting petrol on your diesel engine:

  1. Difficult engine start or failure to start
  2. White smoke coming out from the exhaust pipe
  3. Engine stuttering and stalling
  4. It may clog up spark plugs and fuel systems, causing a misfire and stopping the vehicle from running.
  5. Constant fuel leakage in the combustion chamber
  6. Loss of engine power.

Drain the Fuel Tank

The next step is to drain the fuel tank. Petrol in a diesel engine can cause problems because it reduces the fuel’s lubricity, and petrol burns faster and hotter than diesel.

To avoid damage to your engine, it’s important to drain as much of the contaminated fuel as possible. This process is not as straightforward, as the wrong fuel can damage the fuel’s components. It’s best to leave this job to the professionals.

Here is a step-by-step DIY guide on how to drain a car fuel tank after putting in the wrong fuel:

  1. Drive the car until the fuel level is as low as possible. This reduces the amount of fuel you’ll need to drain.
  2. Park your car in a safe and well-ventilated area. Turn off the engine and allow the car to cool down before draining the tank.
  3. Identify the location of the drain plug. It is typically located under the fuel tank. Use a wrench to loosen and remove the drain plug by turning it counterclockwise.
  4. Place a drain pan under the fuel tank to catch the fuel as it drains out.
  5. Let the fuel drain out completely. This may take a while, depending on the fuel in your tank. Be patient and ensure the fuel is completely drained before proceeding to the next step.
  6. Dispose of the drained fuel properly. Take it to a local recycling center or hazardous waste disposal facility.
  7. Replace the drain plug and fill the tank with the correct fuel. Replacing the fuel filter and checking for any damage to the fuel pump before starting the engine are also recommended.

It is important to note that draining a fuel tank can be hazardous, especially if you are not experienced in automotive repair. If you’re unsure about performing this task, it is best to consult a professional mechanic.

Additionally, consider using a mis-fueling prevention device to avoid such accidents.

Add Diesel and a Fuel Additive

After the fuel tank has been drained, the next step is to add diesel fuel back into the tank. Filling the tank with the right fuel is essential to ensure the engine runs correctly.

However, more than adding diesel alone is required. A fuel additive may also be necessary to clean out any residual petrol in the fuel system.

The fuel additive can help prevent future issues arising from petrol contamination. A professional technician can advise on the right type of fuel additive for your vehicle.

Test the Engine

Once the fuel tank has been drained and refilled with diesel and a fuel additive, the next step is to test the engine. A professional technician will perform a thorough inspection of the engine to ensure that there is no lasting damage.

If there is any damage, it will need to be addressed immediately to prevent further issues from developing. A complete engine flush may also be necessary to remove any traces of petrol left in the engine.


Putting petrol in a diesel engine can be costly, but it doesn’t have to be catastrophic. The most important thing to do is not to start the engine and to have the fuel tank drained as soon as possible.

It’s essential to have a professional technician handle the draining and refilling process to avoid causing further damage to the engine’s components. Adding diesel fuel, a fuel additive, and a thorough engine inspection will help ensure your engine runs smoothly and efficiently.

Following these steps can avoid costly repairs and keep your car running smoothly for years.

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