Dealing with Petrol in Diesel Car: What Steps to Take?

Unless your car is powered by electricity, your vehicle will run on two different types of fuel: diesel or petrol. These types of fuel both work in similar ways as they allow the engine in your car to start; however they’re still different enough that putting the wrong fuel in your vehicle can cause significant issues. 

Known as misfuelling among those in the automotive industry, putting the wrong fuel in your car is much more common than you may think. The AA estimates that over 130,000 people accidentally misfuel their cars every year. This means that it’s a fairly regular incident and is something that you need to be aware of so that it doesn’t happen to you. 

Putting petrol in a diesel car can be costly and cause total engine failure and destruction if you don’t act fast enough. Here’s a bit more information about why misfuelling a diesel car is so bad, as well as some tips and advice on what to do if you’re ever in this situation. If you want some more advice about how to look after your car, you can find plenty of guides on Car Adviser.

In this guide

What happens when you put petrol in a diesel car?

Of the two scenarios, putting petrol in a diesel car is considered a much worse situation than if you did it the wrong way. Annoyingly, misfuelling a diesel car is a lot more common. This is because the fuel inlet is usually a lot larger on models that take diesel. This means that petrol fuel pumps are much more likely to fit into your fuel inlet, meaning that you may not realise that you’re using the wrong fuel until it’s too late. 

When petrol is put into a diesel car, it can react with any leftover diesel in the tank and cause metal parts within your engine system to rub together. This friction and rubbing can cause significant damage, and even a small amount of rubbing can cause things to go wrong. 

Even if you don’t start your car, the mixture of petrol and diesel will still cause issues. If you’re unlucky enough to start your car without realising your mistake, the mixture will work through other parts of your car, causing more widespread damage, which can be costly to repair. 

Some of the major parts of a car that can be damaged through misfuelling a diesel car include: 

The fuel pump

Usually, diesel is used to lubricate a fuel pump in a diesel car, making it more slippery so that parts don’t rub too much. If you accidentally use petrol, there will be much less lubrication, meaning that parts in the fuel pump can rub and break off due to the friction. Not only does this damage the parts, but the metal fragments that have been ground off can travel through your entire fuel system, causing more damage. 

The fuel lines 

If you drive, even a little bit, with petrol in your diesel car, the petrol will travel from the fuel tank through your fuel lines towards your engine. This can clog up the fuel lines, meaning they’ll need to be flushed out. If they’re severely clogged, they may need replacing in the worst-case scenario. 

The filter 

The filter of a diesel car is designed to prevent contaminants from entering your engine, helping to keep it clean and working optimally. If petrol makes its way to the filter, it will no longer work as intended and need to be replaced. 

Fuel injectors 

Although you don’t want any part of your diesel car to be damaged, having issues with your fuel injectors can be one of the most expensive faults due to misfuelling. If metal fragments that have been grounded off from the fuel tank enter your fuel injectors, things can get blocked, ruining the entire system. This could cost thousands of pounds to repair, and you may not even get an insurance payout for damages caused by putting petrol in a diesel car, especially if you’ve driven the vehicle after your mistake.

What shall I do when putting petrol in a diesel car?

The first thing you need to do once you put petrol in a diesel car is to realise your mistake quickly. The sooner you work out that you’ve misfuelled, the better your chance of acting fast and minimising damage. 

You must ensure that you don’t start your engine and leave the car in neutral. This will prevent the petrol from travelling further into your engine system. Hopefully, this will only mean there’s damage to your fuel tank. By not starting your car, you’re not engaging any of the parts, meaning they’re less likely to rub together and break off due to friction. 

If you’ve misfuelled at a petrol pump, you will have to move your car so that you’re not an obstruction for other drivers. To safely move your car without turning it on, you first need to inform staff about your situation and get assistance so that your car can be pushed to a better position where you’re out of the way. 

Once you’re safe, you should call your insurance provider, but only if you have cover for accidental misfuelling. If you do, they’ll be able to organise assistance and cover some, if not all, the costs. However, to ensure that you get covered, you mustn’t turn on your car or drive it in any way. This is because once you drive it, any damage done to your fuel system will be considered intentional by the insurance provider, meaning they may refuse to cover the costs. 

If you don’t have an insurance policy that includes misfuelling, you can instead call your breakdown provider, who will be able to send out roadside assistance and recovery. Depending on your type of cover, you’ll be able to get your car towed to a garage for them to make the necessary repair work. If you don’t have coverage, you can still call a breakdown cover provider to organise assistance, but you may have to pay a one-off fee or register to become a member to get the needed help. You can find reviews and information about many insurance and breakdown providers here on Car Adviser.

If you didn’t realise that you’ve misfuelled your diesel car before you started driving, you must pull over in a safe space as soon as you can. This will limit the damage done to your car and is also a lot safer. This is because petrol in a diesel car can cause engine failure while your car is in motion, which could easily cause you to get into a collision. 

Once you’ve pulled over, you must follow the same steps and contact your breakdown cover provider to deliver your car to a mechanic. When at the mechanic, they can do a few things to help repair your vehicle, depending on how bad the damage is. In the best-case scenario, they’ll need to drain your fuel tank; however, in most cases, you’ll have to get new parts in to replace yours, which can become expensive quickly.

How do I avoid putting petrol in diesel cars in the future?

The best way to handle misfuelling isn’t so much treatment as it is prevention. It’s far better to avoid putting petrol in a diesel car than it is trying to fix it once the issue comes up. Thankfully, there are a few things that you can try in order to make misfuelling a lot less likely in the future. 

One of the best things you can do is to create reminders for yourself so that you’re always conscious and aware of the type of fuel that you need for your car. One of the best ways to do this is by placing reminders in important areas of your car. If your fuel inlet has a cap, it can be a good idea to place a clear sticker in this area that informs you of the type of fuel you need. 

You can also go one further and use a labeller to put a sticker on your dashboard near your fuel gauge. 

When placing stickers in and on your car, ensure that you don’t cover or obstruct anything important and that you don’t put anything in an area that can distract you from driving. 

If you want a more technical solution, buying inlet caps is possible. These gadgets fit around the fuel inlet that leads to your fuel tank and makes the opening the correct circumference for only diesel pumps. With these fitted, it means it’s now impossible for you to put the wrong fuel pump into your car, preventing you from making this mistake in the future. 

In addition to these tips, you can also follow a specific process to ensure you’re not rushed or distracted, which can cause mistakes. 

You should always fuel without distractions. This means that you should leave your phone in your vehicle so that you can seriously focus on what fuel you need. It would help if you also looked for multiple clues that indicate what fuel you’re using. Too many people rely solely on the colour of the pump, which isn’t reliable as the colours can change from fuel station to station. For even better peace of mind, follow the hose to see which pump it’s connected with to ensure it’s diesel.

Diesel in Petrol Car FAQs

Most misfuelling cases happen with people putting petrol in a diesel car. This is because the nozzle is much smaller, meaning it's more likely to fit into a diesel car's fuel inlet. A diesel pump is much larger, meaning it's unlikely to fit into a petrol car's inlet, making it much less common, as people are much more likely to realise that they've made a mistake in this scenario. 

There are about 130,000 instances of misfuelling in the UK a year, according to the AA. This means there are around 364 cases of misfuelling around the country every day. That may not seem like a lot, but these numbers suggest that it's a frequent issue and something you need to be aware of to avoid. 

In addition to misfuelling, another common issue people make at petrol stations is accidentally putting AdBlue into their fuel tank. This is an exhaust fluid that's designed to help diesel cars meet the latest regulations regarding emissions. Putting AdBlue into a fuel tank is becoming far more common, so it should be something that you're wary of too. 

If you accidentally put AdBlue or any other type of exhaust fluid into your fuel tank, you could cause costly damage to your fuel tank, pump, and injection system. 

The best thing you can do if you're in this situation is to not turn on your engine, as this initial combustion is what will cause massive damage to your car, resulting in an enormous repair fee. 

If you haven't realised that you put petrol in a diesel car, then there will be a few signs that will make it clear that you've made a mistake. 

The most common symptom is that the car will make a knocking sound when accelerating, getting louder the faster you go. You may also notice that the exhaust will produce much more excess smoke than usual, typically a tell-tale sign of something wrong with your engine. 

You may also find that idling your car is much more rough and bouncy, and you could also see that accelerating is tough to do and that the car doesn't increase speed as quickly as it would have done if it was healthy. 

After a while, you may also notice that the engine warning light will come on, which is something that you should never ignore. After prolonged driving with the wrong fuel, your engine will likely stop, and it may not start again, especially if it's warm. 

With all that said, you should realise that you've made a mistake when fueling before all of these symptoms become apparent, as they will indicate that the repairs will be expensive and take a long time.

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