What happens when you put petrol in a diesel car?

If you’re at a pump and in a hurry, or you’ve accidentally added the wrong fuel, it can be 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 right steps to fix it.

In this guide, we will cover what to do immediately and the next steps.

Don’t start the engine: Do not start your car. If you have already started it and then realise it, stop your engine immediately.

Move your car to a safe space: Keep your vehicle in neutral and have someone assist you in moving it to a safe location.

Seek Professional Help: Contact a tow truck to take the vehicle to a mechanic.

Drain the Fuel Tank: The fuel system must be professionally drained and flushed to remove contaminated fuel.

Replace Fuel Filters: It’s essential to replace the fuel filters. By replacing them, you can effectively block the passage of contaminated fuel.

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, e.g., around 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.

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

You added petrol to a diesel tank, which is a much bigger mistake and requires extensive flushing and cleaning.

You added diesel to a petrol tank, which is less serious and cannot cause permanent damage, but it still needs to be properly flushed.

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.

Misfueling can break or damage several key components  of a vehicle if the engine is started. I

t can affect the entire fuel system, including the high-pressure pump, injectors, lines, filters, pistons, cylinder walls and catalytic converters.

Repair costs can add up to thousands of dollars.

In such cases, sourcing reusable parts from car wreckers can be a cost-effective solution for repairing the entire fuel system within a budget.

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.

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 check online on 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.