What Happens When You Put Petrol In A Diesel Car

If you’re at a pump and in a hurry or have accidentally added the wrong fuel, it can be both embarrassing and stressful. This mistake is quite common and can lead to engine damage. However, there’s no need to panic; stay calm and take the necessary steps to address the issue. In this guide, we will learn what to do immediately and detail the following steps.  

What You Should Do Immediately?

1. Don’t start the engine: Do not start your car. If you have already started it and then realise it, stop your engine immediately.
2. Move your car to a safe space: Keep your vehicle in neutral and have someone assist you in moving it to a safe location.
3. Seek Professional Help: Contact a tow truck to take the vehicle to a mechanic.
4. Drain the Fuel Tank: The fuel system must be professionally drained and flushed to remove contaminated fuel.
5. Replace Fuel Filters: It’s essential to replace the fuel filters. By replacing them, you can effectively block the passage of contaminated fuel.

Understanding The Difference Between Petrol & Diesel Engines

Petrol & diesel engines may look similar, but their functionalities are totally different. A petrol engine uses a spark plug to ignite a pre-mixed fuel and air mixture. The compression ratio for a petrol engine is lower, around e.g., 10:1.

Diesel engines rely on compression—the air inside the cylinder is compressed until it becomes hot enough to ignite the injected fuel on its own. The compression ratio for a diesel engine is higher, around e.g., 18:1.

Diesel fuel is thicker than petrol and contains more energy per litre, which helps deliver better torque and fuel efficiency.

On the other hand, petrol is lighter in weight and burns cleaner and more quickly, but doesn’t provide the same level of lubrication. That’s why putting petrol in a diesel car can cause serious damage— petrol removes the lubrication that diesel parts need to function smoothly.

Petrol In a Diesel Engine Vs. Diesel In Petrol Engine – Which Is More Damaging?

There are two possible problems when you accidentally fill the wrong fuel:

• You have added petrol to a diesel tank, which is a much bigger mistake, requiring extensive flushing and cleaning work.
• You have added diesel to a petrol tank, which is a less serious problem and can’t cause any permanent damage, but it still needs to be properly flushed.

What Happens When You Accidentally Do That?

Accidentally putting petrol into a diesel car can cause severe engine damage.

• Lack of Lubrication: Diesel engines rely on the fuel to lubricate and operate the high-pressure diesel fuel pump, and petrol disrupts this process. This causes increased friction, leading to the metal parts of the pump disintegrating and creating metal fragments.
• Fuel System Contamination: And the metal fragments then travel through fuel lines, the injector and filters. This contamination can block the system, reduce fuel pressure, or make the engine run unevenly or stop altogether.  
• Engine Damage: The lack of proper lubrication and fuel system contamination can lead to complete engine failure.

When the Damage is Beyond Repair

If your car is old or the engine repair cost is higher than the car’s actual value, then selling it to a wrecker makes more sense. Wreckers accept cars or any vehicles in any condition. If the car is beyond repair, then choosing a cash for cars service is a more practical and hassle-free solution.

Why is it a Common Mistake?

Adding petrol to a diesel engine is the most common mistake. It usually happens when you drive your friend’s office or rental vehicle. If you recently changed your vehicle and now have a diesel engine, but previously had a petrol engine, and you didn’t have a habit of.

Why is it a Costly Mistake?

Repairs for putting petrol in a diesel car can be expensive and could take thousands of dollars (from $200-$10,000), as they may require replacing the entire fuel system, including the high-pressure pump, injectors and filters.

How To Prevent Misfuelling In Future?

There are a few ways to avoid these types of mistakes in the future:

• Always double-check the nozzle label.
• Use a different colored fuel cap, such as a sticker, inside the car.
• Keep focus while fueling, especially when renting or using multiple vehicles.
• If you’re driving someone else’s car, make sure to ask the person about the fuel type, or you can check online via the Carjam site.
• Carefully read the pump’s trigger label and the fuel grade indicator.
• Don’t get fuel in a hurry, when you’re hungry or stressed—you’re more likely to make a mistake at that time.