Petrol in Diesel Car: What to Do

Misfuelling: The Common Mistake You Need to Know About

It's a mistake that many drivers unfortunately make at some point: filling your car with the wrong type of fuel. Whether it's petrol in a diesel engine or diesel in a petrol engine, this error can lead to significant damage and costly repairs. In the UK, it's estimated that up to 150,000 people misfuel their cars every year, meaning it happens every three minutes! Even the police force has faced substantial bills due to this common oversight. This article aims to provide comprehensive information on what to do if you've put petrol in your diesel car, the potential consequences, and how to prevent this from happening again.

Why Does Misfuelling Happen?

Life in the modern age is incredibly busy. With tight schedules and the constant pressure to be efficient, people often find themselves rushing. This haste can lead to simple yet costly mistakes, and misfuelling is a prime example. Other contributing factors include:

• Changing Vehicles: Drivers who switch between petrol and diesel cars can sometimes revert to old habits, filling the new car with the fuel type they are accustomed to.
• Rental Cars: Those driving rental vehicles might be used to a particular fuel type and mistakenly fill the rental with the wrong one.

Understanding Fuel Types and Engine Differences

Understanding the fundamental differences between petrol and diesel engines is crucial to grasping why misfuelling is so problematic. Here's a breakdown:

Petrol Engines

Petrol engines work by igniting a mixture of air and fuel using a spark plug. They require fuel with a high octane rating and a low cetane rating for optimal performance. They rely heavily on spark plugs to initiate combustion.

Diesel Engines

Diesel engines operate differently. They compress air to a high temperature, and then inject diesel fuel, which ignites due to the heat and pressure. They do not use spark plugs. Diesel engines perform best with fuel that has a low octane rating and a high cetane rating.

The Impact of Petrol in a Diesel Engine

Putting petrol into a diesel tank is a common scenario, often facilitated by the fact that petrol nozzles are typically smaller and can fit into diesel filler necks. The consequences can be severe:

• Lubrication Loss: Diesel fuel acts as a lubricant for the diesel engine's components, particularly the fuel pump and injectors. Petrol, however, has solvent-like properties and strips away this essential lubrication.
• Component Damage: Without proper lubrication, the high-pressure fuel pump and injectors can suffer significant wear and tear, potentially leading to seizure.
• Seal Degradation: Petrol can degrade the seals within the fuel system, causing leaks and improper fuel delivery.

What Happens if You Put a Small Amount of Petrol in Diesel?

If you've only put a small quantity of petrol into your diesel tank, the situation might be less catastrophic. In older vehicles, a small amount of petrol was sometimes added to diesel in winter to prevent freezing. However, this is not recommended practice. If you've made this mistake, filling the rest of the tank with the correct diesel fuel can help dilute the petrol. It's advisable to keep the fuel level topped up and drive normally, allowing the mixture to pass through the system gradually. However, for larger amounts of petrol, draining the tank is the safest course of action.

Signs of Petrol in a Diesel Tank

If you've inadvertently put petrol in your diesel car and driven it, you might notice the following symptoms:

• Difficulty starting the engine, especially if it's warm.
• Unusual engine noises, particularly under load.
• Excessive smoke from the engine or exhaust pipe while driving.
• Loss of power or engine stuttering.

The Impact of Diesel in a Petrol Engine

While less common due to nozzle size differences, putting diesel into a petrol car is also a serious mistake. Diesel is a heavier, more viscous fuel than petrol:

• Fuel System Contamination: Diesel can clog fuel filters and injectors in a petrol engine, preventing proper fuel delivery.
• Engine Misfire: The engine may start to misfire, run rough, or cut out entirely.
• Severe Damage: In modern direct injection petrol engines, diesel can cause more significant damage if the engine is run for any length of time.

Signs of Diesel in a Petrol Tank

If you've put diesel in a petrol car, you might observe:

• The engine failing to start or struggling to start.
• The engine misfiring or running erratically.
• The engine cutting out unexpectedly.
• Excessive smoke from the engine bay and exhaust.

What To Do Immediately If You Misfuel

The most critical action to take is to prevent further damage. Here's what you should do:

1. Do NOT Start the Engine: If you realise your mistake at the pump, do not turn the ignition on or start the engine.
2. Do NOT Drive the Car: Even if you've already started it, turn it off immediately and do not attempt to drive it.
3. Inform Station Staff: Alert the petrol station staff about your mistake.
4. Disconnect the Battery (if necessary): If you need to move the car a short distance to a safer spot, consider disconnecting the battery to prevent accidental ignition.
5. Contact Roadside Assistance: Call a professional wrong fuel recovery service. They have the equipment to drain your fuel tank safely and efficiently.

Potential Repair Costs and Insurance

The cost of rectifying misfuelling can vary significantly depending on how quickly the mistake is identified and addressed:

• Drain and Flush Only: If caught immediately before starting the engine, draining and flushing the contaminated fuel can cost between £120 and £250.
• Minor Repairs: If the car has been driven for a short distance, repairs might involve replacing fuel filters, and cleaning fuel lines, costing around £1,000 to £2,000.
• Major Repairs: Driving a significant distance can lead to damage to the fuel pump, injectors, and potentially the engine itself, resulting in bills from £5,000 to £6,000, or even more in severe cases.

Insurance policies and vehicle warranties typically do not cover misfuelling. Roadside assistance services, while they can help, will usually charge separately for this specific service as it falls outside standard breakdown cover.

How to Avoid Misfuelling in the Future

Preventing misfuelling is far better than dealing with the aftermath. Here are some practical tips:

• Read the Pump Labels Carefully: Always double-check the label on the fuel pump before you start filling.
• Be Aware of Nozzle Colours: While colour coding exists, it's not always consistent or reliable.
• Leave Reminders: If you've recently switched to a different fuel type, place a reminder note on your dashboard or fuel cap.
• Avoid Distractions: Refuel when you are not rushed, stressed, or distracted by mobile phones or other passengers.
• Consider a Fuel Filter Funnel/Adapter: Specialised funnels or adapters can prevent the incorrect nozzle from entering your fuel filler neck. Some are designed to only accept the correct nozzle size. Investing in one of these, costing around £15-£30, can save thousands in potential repair bills.

Repairs Involved in Misfuelling Recovery

Depending on the severity, repairs can include:

• Draining and flushing the fuel tank and lines.
• Replacing fuel filters.
• Replacing the fuel pump.
• Replacing fuel injectors.
• Cleaning or replacing spark plugs (for petrol engines).
• Repairing or replacing seals and O-rings.

Choosing the Right Wrong Fuel Recovery Service

While major breakdown providers like the AA and RAC can assist, their costs for misfuelling recovery can be higher, and they may subcontract the work. Smaller, specialised "wrong fuel drain" companies often offer a more competitive price and quicker response times. When choosing a service, consider:

• Price: Compare quotes from different providers.
• Response Time: How quickly can they reach you?
• Availability: Do they operate 24/7?
• Customer Reviews: Look for reputable companies with positive feedback.

While specific company endorsements are subjective, prioritising a service that is transparent about pricing, offers a prompt response, and has good customer reviews is essential. Companies like GMM1 are often cited for their competitive pricing and efficient service.

Frequently Asked Questions

Q1: What happens if I put a little petrol in my diesel car and drive it?
Driving with petrol in a diesel car can cause the fuel system to lose lubrication, leading to damage to the fuel pump and injectors. You might also experience poor performance and increased smoke.

Q2: Can I claim misfuelling on my car insurance?
Generally, no. Most insurance policies explicitly exclude damage caused by misfuelling.

Q3: How long does it take to drain a fuel tank?
A professional fuel drain typically takes around 30-60 minutes, depending on the vehicle and the amount of fuel to be removed.

Q4: Will my breakdown cover pay for wrong fuel?
Standard breakdown cover usually does not include misfuelling. You will likely be charged separately for this service.

Q5: Is it safe to put petrol in a diesel car in winter?
While historically a small amount of petrol was added to prevent diesel from freezing, it is not recommended with modern vehicles as it can damage the fuel system.

By understanding the risks and taking immediate, correct action, you can minimise the damage and cost associated with misfuelling your vehicle.

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