Misfuelling: What Happens if You Fill Your Car With the Wrong Fuel

Putting the wrong type of fuel into your vehicle - known as 'misfuelling' - is an easily made and potentially costly mistake made by many motorists. Recent statistics estimate that around 150,000 vehicles in the UK are filled with the wrong fuel every year. 

The most common mistake made by drivers is petrol being pumped into diesel engine cars, although putting diesel into petrol vehicles, or using the incorrect petrol grade (regular instead of premium, for example), also qualifies as misfuelling. The consequences can range from expensive repairs to invalidated warranties. 

This article explores the common causes of misfuelling, steps you can take to avoid making this mistake, what to do if you have put the wrong fuel in your car, and how much it would cost to repair. Read on to find out more… 

What does misfuelling mean?

Misfuelling refers to putting the wrong type of fuel into a vehicle. The most common types of misfuelling are:

• Putting petrol into a diesel engine vehicle - Diesel vehicles run on diesel fuel and putting petrol into them can cause serious damage to the fuel system and engine.
• Putting diesel into a petrol engine vehicle - Petrol vehicles require petrol to run and putting diesel into them can also lead to fuel system and engine damage.
• Using the wrong octane rating of petrol - Using a lower octane petrol than a vehicle is designed for can cause problems as well as potential engine damage over time. Similarly, using a higher octane rating than required is generally not an issue but is a waste of money.
• Accidentally mixing petrol and diesel in the same vehicle - Whether this occurs by pouring petrol on top of diesel or vice versa, mixing fuels can cause immediate breakdowns and extensive repairs being required.

What happens if you fill your car with the wrong fuel?

Here are some of the issues that can happen if you accidentally fill your car with the wrong type of fuel:

Engine stalling or refusing to start

Putting petrol in a diesel car or vice versa will usually result in the engine not starting or stalling almost immediately. This prevents damage from occurring but often requires the tank to be drained before the car can be used again.

Fuel system damage

The wrong fuel can corrode and damage fuel lines, injectors, pumps and filters that are specifically designed for either petrol or diesel. Replacing them can be extremely costly.

Engine knocking or pinging

If the wrong petrol grade is used, persistent engine knocking can occur and cause long-term wear and tear on key engine components.

Catalytic converter damage

The catalytic converter helps filter exhaust emissions but works best with the right fuel. Misfuelling can lead to overheating and a subsequent meltdown of this expensive component.  

Full engine failure

In a worst-case scenario, filling and then driving with the incorrect fuel circulating in your engine can completely ruin it, requiring a full replacement.

Voided warranty

If your vehicle is new and still has a valid warranty, it is unlikely the company will cover the damage caused by putting in the wrong type of fuel. This could leave you with potentially huge bills for repair and replacement.

What should you do if you accidentally put the wrong fuel in your car?

Here are our recommended six steps to take if you accidentally put the wrong fuel in your car:

1. Stop immediately and turn off the engine - As soon as you realise you have misfuelled, stop driving immediately and turn off the engine. This will help minimise the amount of damage caused by the wrong fuel circulating through the fuel system.

2. Check the fuel filler cap for warnings - There may be stickers on the cap or surround indicating what fuel type your car requires. This will confirm if petrol has gone into a diesel engine or vice versa.

3. Call for assistance - Call professional breakdown recovery services who will have the expertise in dealing with misfuelling incidents. Follow their advice carefully regarding what to do next. Do not try to drive the vehicle anywhere and instead wait for assistance to come to you.  

4. Have the fuel tank fully drained - In most cases, arranging fuel drainage and flushing of the tank, fuel lines and filters is required to remove all traces of the incorrect fuel. This may need to happen on-site or at a vehicle service centre.

5. Further system checks and repairs - Once drained, diagnostics should check for any lasting damage caused. Some fuel system components like injectors or seals may need replacing following contamination.

6. Refuel with the proper fuel - Finally, make sure that the correct fuel for your vehicle is used when refuelling after the incident.

The most important steps following misfuelling are to stop driving the car, call for assistance and get the fuel tank fully drained to avoid any permanent car problems. REMEMBER: Prevention remains better than cure when it comes to misfuelling mishaps! 

How much does it cost to repair misfuelling?

The cost to repair a vehicle that has been misfuelled can vary considerably but often runs into the hundreds or thousands of pounds. With average repair bills estimated at around £1,344, putting the wrong fuel in a vehicle can be expensive. Here is a breakdown of some typical costs involved:

• Fuel drainage and flush: £50 - £150

This involves draining out the contaminated fuel and flushing the fuel tank and system with fresh fuel or mechanical cleaning. 

• Fuel system repairs: £500 - £1,500+ 

If misfuelling damage has occurred then repairs or full replacement of fuel system components like injectors, seals, pumps and filter systems may be required.

• Engine repairs: £1,000 - £5,000

In the worst case, major engine components can be fully destroyed by the wrong fuel causing knocking, overheating or corrosion. A full engine replacement could cost up to £5,000 for parts and installation.

• Catalytic converter: £500 - £1,000  

Another consequence of misfuelling is the destruction of the catalytic converter which is there to regulate exhaust emissions.

Is misfuelling covered by car insurance?

Typically, misfuelling a car is not covered under standard UK car insurance policies. Insurance policies are designed to cover accidental vehicle damage, theft and liability to others - but putting the wrong fuel into your car is usually classified as 'self-inflicted' damage.

Most insurers will dispute and refuse misfuelling claims on the grounds that the action falls under driver negligence and error. Additionally, many policies contain specific small print exclusions stating misfuelling incidents and any resultant repairs will not be paid out. 

Misfuelling repairs at EMG Motor Group

If you’re a motorist in East Anglia who has accidentally filled your car with the wrong fuel, then fear not, at EMG Motor Group we are here to help. Our specialist service team are experienced in the repair and maintenance of many makes and models. Get in touch with us to discuss your misfuelling mistake.