Accidentally putting diesel in a petrol car is an easy mistake to make, especially when you’re distracted at the fuel station. While it may seem like a harmless error, this mistake can have serious consequences for your vehicle if not addressed promptly. Knowing what to do in such a situation can help mitigate damage and save you costly repairs. Below, we provide a comprehensive guide to what happens when you fill up a petrol car with diesel, what to do immediately, and how to prevent long-term damage.
What Happens When You Put Diesel in a Petrol Car?
Filling a petrol engine with diesel can cause significant harm because diesel fuel is denser and heavier than petrol. Petrol engines rely on the vaporization of fuel for combustion, and diesel does not vaporize in the same way. When diesel in petrol cars enters the system, it can clog up various engine components, including fuel injectors and filters, potentially causing severe damage. Diesel fuel can also lead to misfiring and, in the worst-case scenario, engine failure.
Immediate Signs of Diesel in a Petrol Car
- Difficulty Starting the Engine – Diesel fuel will not ignite in a petrol engine. If you’ve filled up with diesel, the car may struggle to start or not start at all.
- Loss of Power – If the car does start, you may notice a loss of power or stuttering as the diesel moves through the fuel system.
- Excessive Smoke – The incorrect fuel can cause excessive exhaust smoke, a clear sign that something is wrong.
- Engine Warning Lights – In many modern vehicles, the engine management system will detect the wrong fuel and activate warning lights.
Steps to Take Immediately After Filling Diesel in a Petrol Car
1. Don’t Start the Car
The most important thing to do when you realize you’ve put diesel in a petrol car is to avoid starting the engine. If the engine hasn’t been turned on, the damage can be minimized since the fuel remains in the tank and hasn’t reached the more sensitive engine components.
2. Move Your Vehicle to a Safe Spot
If you’ve already started the car and it stalls, shift the vehicle to a safe location using neutral gear. It’s crucial to prevent the diesel from circulating further into the system.
3. Call for Professional Assistance
Attempting to fix the issue yourself can be dangerous and lead to further complications. We recommend contacting a roadside assistance service or a professional mechanic who specializes in fuel drainage. They will likely drain the tank, flush the fuel lines, and remove any residual diesel in petrol car systems.
Potential Damage to Your Vehicle
The extent of damage caused by putting diesel in a petrol car depends largely on how quickly the problem is addressed. If the car hasn’t been started, you’re in luck—draining the fuel tank and cleaning the fuel system should resolve the issue. However, if the engine has been running on diesel, more extensive damage may occur. Common issues include:
- Clogged Fuel Injectors – Diesel can cause injectors to clog, resulting in poor fuel delivery.
- Damaged Fuel Pump – Diesel’s denser composition can stress a petrol fuel pump, leading to malfunction.
- Contaminated Spark Plugs – Diesel can foul spark plugs, requiring them to be cleaned or replaced.
- Exhaust System Problems – Diesel can clog the catalytic converter, leading to expensive repairs.
In severe cases, you may need to replace parts of the fuel system or, in extreme situations, the engine itself. Immediate action is essential to prevent these costly repairs.
Preventing the Mistake in the Future
1. Pay Close Attention at the Pump
Most modern petrol pumps are color-coded to help prevent fueling mistakes. Diesel pumps typically have a black nozzle, while petrol is usually green. Being mindful of these color differences can help avoid confusion.
2. Label Your Fuel Cap
If you frequently switch between petrol and diesel vehicles, consider labeling the fuel cap or using a reminder sticker to avoid mistakes. This is a simple, effective solution for drivers who are at a higher risk of filling with the wrong fuel.
3. Use a Fuel Guard System
Some aftermarket devices can be installed in your fuel tank to prevent the insertion of the wrong fuel nozzle. These systems are relatively inexpensive and offer peace of mind.
What Happens If You Drive on Diesel in a Petrol Car?
If you drive the car after accidentally filling it with diesel, the situation becomes more complicated. Diesel fuel can enter the combustion chamber, where it cannot ignite properly, causing severe damage. Here are some common symptoms and their associated problems:
- Engine Knocking – A knocking noise from the engine often indicates that the diesel is not being combusted properly.
- Reduced Engine Performance – You may experience sluggish acceleration and reduced overall performance.
- Check Engine Light – Driving with diesel in a petrol car will usually trigger the vehicle’s diagnostic system, causing the check engine light to come on.
Driving for prolonged periods with the wrong fuel can cause lasting damage, requiring extensive repairs to the fuel injectors, catalytic converter, or even the entire engine. If you suspect you’ve driven with diesel in a petrol car, stop driving immediately and call a professional for assistance.
How to Minimize Costs and Repairs
The key to minimizing costs is to act quickly. If you haven’t started the car after filling it with diesel, the cost is usually limited to draining the fuel tank, which ranges from $200 to $400, depending on your location and the vehicle type. However, if the diesel has been circulated through the engine, repairs can cost thousands of dollars. To avoid unnecessary expenses:
- Act Immediately – Do not delay in seeking help. The sooner the fuel is drained, the less damage is done.
- Use a Specialist – Look for a mechanic or roadside service with experience in fuel system flushing and repairs.
Conclusion
Accidentally filling up with diesel in a petrol car is a mistake that can happen to anyone. However, knowing the signs and taking quick action can prevent significant damage to your vehicle. The most important thing to remember is not to start the car after realizing the mistake. If the vehicle has been started, stop driving as soon as possible and call a professional for assistance. With the right approach, you can minimize the damage and avoid costly repairs.
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