What Happens If You Put Petrol in a Diesel Car? A Comprehensive Guide
Putting petrol (gasoline) in a diesel car is a common and costly mistake. This error can lead to significant engine damage if not addressed promptly. Understanding the differences between petrol and diesel fuel, and the consequences of this mix-up, is crucial for any vehicle owner. This article will delve into the mechanical repercussions, immediate signs, and the necessary steps to take if you make this critical error.
The Fundamental Fuel Differences
Diesel engines and petrol engines operate on fundamentally different principles, primarily due to their fuel types. Diesel fuel is a heavier, oilier substance that ignites under high compression within the engine cylinder. Petrol, on the other hand, is a lighter, more volatile fuel that requires a spark plug to initiate combustion. This core difference is why mistakenly filling a diesel tank with petrol can cause severe problems.
Why Petrol is Harmful to Diesel Engines
Petrol lacks the lubricating properties of diesel fuel. The high-pressure fuel pump and injectors in a diesel engine rely on the viscosity of diesel to keep them lubricated. Petrol, being much thinner, will strip away this vital lubrication, leading to friction, overheating, and eventual failure of these critical components. Furthermore, petrol ignites at a much lower temperature and pressure than diesel. When introduced into a diesel engine’s high-compression environment, it can lead to uncontrolled combustion or “knocking,” which can cause internal engine damage.
Immediate Signs of Petrol Contamination
The moment you start the engine after accidentally filling it with petrol, you might notice several alarming symptoms. These signs are the car’s way of telling you that something is seriously wrong.
* **Difficulty starting:** The engine may struggle to turn over or refuse to start altogether.
* **Rough idling and stalling:** Once started, the engine will likely run very roughly, hesitate, and may stall frequently.
* **Unusual noises:** You might hear knocking, rattling, or a “screaming” sound from the engine.
* **White or blue smoke:** The exhaust may emit excessive white or blue smoke.
Fact: Diesel fuel has a higher energy density than petrol, meaning it stores more energy per unit volume. This contributes to diesel engines’ typically better fuel efficiency.
The Mechanical Damage Explained
The damage caused by putting petrol in a diesel car can be extensive and expensive. The severity often depends on how much petrol was added and how far the car was driven before the issue was identified.
Fuel System Damage
The most immediate and common damage occurs within the fuel system:
* **Fuel Pump Failure:** As mentioned, the lack of lubrication in petrol will quickly wear down the high-pressure fuel pump, leading to its complete failure.
* **Injector Damage:** Diesel injectors are precision-engineered. Petrol can cause them to seize up, corrode, or fail entirely.
* **Fuel Lines and Seals:** Petrol can degrade rubber and plastic components within the fuel system, causing leaks.
Engine Internal Damage
If the car is driven with petrol in the tank, the damage can extend to the engine’s internal components:
* **Piston and Cylinder Damage:** The uncontrolled combustion caused by petrol can lead to severe stress on pistons and cylinder walls, potentially causing cracks or scoring.
* **Bearing Damage:** Knocking and excessive vibration can damage engine bearings.
What To Do If You Make the Mistake
Discovering you’ve put petrol in your diesel car can be panic-inducing, but acting quickly and correctly is paramount.
1. **DO NOT START THE ENGINE:** This is the most critical step. If the engine is off, the petrol is likely confined to the tank and hasn’t circulated through the fuel system.
2. **Call for a Tow Truck:** Do not attempt to drive the car. Have it towed to a qualified mechanic or a specialist diesel repair shop.
3. **Inform the Mechanic:** Clearly explain what has happened – the type of car, the amount of fuel added incorrectly, and whether the engine was started.
The Repair Process
A mechanic will need to take several steps to rectify the situation:
* **Drain the Fuel Tank:** The entire contents of the fuel tank must be drained and disposed of properly.
* **Flush the Fuel System:** The fuel lines, fuel filter, and fuel rails will need to be thoroughly flushed to remove any residual petrol.
* **Replace Fuel Filter:** It’s standard practice to replace the fuel filter to ensure no contaminants remain.
* **Inspect and Repair/Replace Components:** The mechanic will inspect the fuel pump and injectors for damage. Depending on the extent of the damage, these parts may need to be repaired or replaced.
* **Clean or Repair Engine Components:** If the engine was run, further inspection and potential cleaning or repair of internal components may be necessary.
Here’s a summary of potential repair costs:
| Component Replaced | Estimated Cost (USD) |
| :—————– | :——————- |
| Fuel Drain & Flush | $200 – $500 |
| Fuel Filter | $50 – $150 |
| Fuel Pump | $500 – $2000+ |
| Injectors (each) | $200 – $1000+ |
| Engine Repair | $1000 – $5000+ |
Preventing the Mistake
Preventing this error is far easier and cheaper than dealing with the consequences.
* **Double-Check the Pump:** Always confirm the pump you are using dispenses diesel (usually green handles or labels) and that you are selecting the correct fuel type for your vehicle.
* **Know Your Vehicle:** Be aware of whether your car is petrol or diesel.
* **Refuel in Daylight:** Poor lighting conditions can increase the chance of error.
* **Ask for Help:** If you are unsure, ask a service station attendant for assistance.
Remember:
> A moment of inattention at the fuel pump can lead to weeks of repair time and significant financial cost.
Frequently Asked Questions
What if I only put a small amount of petrol in a diesel tank?
Even a small amount of petrol can be detrimental due to its lack of lubricity. If the amount is very small (e.g., less than a litre in a large tank) and the engine is not started, the risk might be lower, but it’s still advisable to seek professional advice or at least have the tank drained.
How much does it typically cost to fix?
The cost can range from a few hundred dollars for a simple drain and flush to several thousand dollars if the fuel pump, injectors, or internal engine components need replacement.
Can I drive my car if I accidentally put petrol in it?
Under no circumstances should you drive a diesel car after putting petrol in the tank. Starting the engine allows the contaminated fuel to circulate, significantly increasing the risk of severe and costly damage.
In conclusion, the act of putting petrol in a diesel car is a serious mechanical mishap with potentially severe consequences. The fundamental differences in fuel properties, particularly lubrication and ignition, mean that petrol acts as a damaging agent within a diesel engine’s sensitive fuel system and combustion process. Immediate recognition of the symptoms and prompt, decisive action – primarily by not starting the engine and seeking professional towing and repair – are vital to mitigate the damage. While repairs can be extensive and costly, understanding the process and preventative measures can save vehicle owners from a significant amount of stress and financial burden. Always remain vigilant when refuelling to avoid this common yet damaging error.
