Misfuelling Guide for Diesel in a Petrol Car

When refilling a car, the vehicle will use one of two different types of fuel: petrol and diesel. Although they’re both somewhat similar in function, as they help facilitate the combustion within an engine, they’re both different enough that putting the wrong type of fuel in a car can cause severe damage to the vehicle and make it much harder for the engine to start.

You may think that misfuelling (the name for when you put the wrong fuel in your car) is uncommon, but the truth is over 130,000 misfuelling incidents happen in the UK every year, making it a reasonably regular incident, so it should be something that you think about when you go to refill your car.

Typically, diesel is used to power heavier vehicles like trucks and Jeeps, whereas petrol is best suited to smaller vehicles and is the more common type of car fuel. Getting your fuel wrong can be a significant issue, here’s more information about why it’s terrible for your car, as well as some tips from Car Adviser about what you should do if this happens to you. 

In this guide

What happens when you put diesel in a petrol car?

Thankfully, putting diesel in a petrol car isn’t as bad as getting it the other way around. It may not cause irreversible damage to the engine, but it can still cause issues and result in you needing to get repairs, and it can also seriously disturb your plans for the day.

If you’ve not yet started the car after putting in diesel instead of petrol, then there won’t be any signs of physical damage. However, once you start the car, you may find that the engine will start smoking and produce a burning smell. The engine may also cut out and stop completely. When trying to restart your car, you may notice some misfiring due to the spark plugs being coated by the diesel. 

Because petrol cars use a spark to ignite the fuel within your engine, if this is clogged up, there won’t be a spark, meaning that your engine will likely not start or quickly stop if it manages to fire. 

Thankfully, you’ll likely avoid any permanent damages when accidentally putting diesel in a petrol car, meaning that this issue isn’t that serious for most people.

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

You need to do a few things to help maximise the chances of your car being successfully repaired after putting the wrong fuel in your petrol car. 

Firstly, if you’ve noticed that you’ve misfuelled and put diesel in your petrol car before you drive off, you mustn’t start your car. This is because starting the engine will cause some components to be covered by the diesel, making it harder to fix in the future. If you’re blocking a pump bay and need to get out of the way, put your car in neutral and inform the staff what you’ve done. They will be able to provide assistance and help you push your vehicle to a better, more convenient location where you can wait for further assistance. 

If you’ve set off and haven’t noticed, the next best thing is to find the nearest place where you can safely pull over and then turn off your ignition. You must do this as quickly as you can, as having the engine on for longer will cause more problems and increase the likelihood for the engine to cut out, which can be unsafe when driving on the road. 

Once you’ve pulled over, you need to get help. If you have misfuelling covered as part of your insurance policy, you should call your insurance provider to get assistance. If it’s not covered – which is likely in most cases – you’ll have to contact your breakdown cover provider instead. When you do this, they’ll get someone to come to your location to provide roadside assistance and recovery, where you’ll be towed to the nearest mechanic. 

If you don’t have a breakdown cover, you’ll need to call a breakdown company to get help. You’ll either have to pay a call-out fee and the total cost of the repairs, or you’ll have to become a member first before you can get help. 

Once the car has been towed to a garage, it will be cleaned and drained to remove the diesel. If there is any additional damage, the mechanic will also fix this, although you’ll have to pay for this additional work too. 

When dealing with putting diesel in a petrol car, the most important thing is not to start it. This will minimise any damages and will simply mean that the engine will need to be drained, cleaned, and refilled, and you’ll likely avoid any permanent damages. 

How to avoid putting diesel in a petrol car in the future?

Out of the two misfuelling scenarios, putting diesel in a petrol car is far less likely. This is because most diesel pumps will be too big to fit correctly in a petrol car, making it very unlikely that you’ll be able to fuel it anyway.

However, as it can still happen, there are a few steps that you can take to ensure that you’ll never be caught in this situation again. 

The most common way to avoid misfuelling is to install a prevention cap on your car. This will ensure that only the nozzle for petrol can fit into your vehicle. If your fuel inlet was big enough to fit the diesel pump before, it would be a great way to make it much less likely for you to get it wrong. 

A prevention cap can be installed at the top of your fuel inlet and will reduce the circumference of the gap, only allowing petrol pumps to fully enter and fuel the tank. This device usually isn’t that expensive and can be installed in just a few minutes. 

In addition to gadgets, you can also be more obvious and create a reminder for you that you can see every time you fill up your car. This will ensure that the type of fuel you’re using is on your mind, which could help you be more careful. 

If you have a lid for your fuel cap, you could always get a sticker and place it on the inside to tell you what type of fuel the car takes. You could also use a labeller to put a reminder on your dashboard near your fuel gauge. If you’re going to do this, make sure that you place it in a location where the sticker doesn’t obstruct any other types of information. 

Modifying your vehicle and creating reminders may seem excessive ways to prevent future misfuelling. Still, they could be invaluable pieces of advice if they stop you from having to pay a lot of money to get your car recovered and repaired. 

You can also take a few other steps to ensure that you don’t misfuel again. One of the main things you can do is to ensure that you’re not relying on the colour of the hose or nozzle to help you distinguish between petrol and diesel. This is because different petrol stations can use different colour systems. You should also fully pay attention to the pump’s trigger label and fuel grade indicator to ensure you’re not making a mistake. 

Most of the time, people make misfuelling mistakes because they’re distracted or in a hurry. If you’re in this situation, it’s best to remove distractions like your phone and slow down the process to ensure that you’re doing everything properly. 

To make any future issues more bearable, it’s important to get an insurance policy where misfuelling is included, as this can help save you money and make it easier to access the required help. You should also consider breakdown cover, as even their basic plans will provide you roadside assistance and recovery to the nearest mechanic, which can make this issue a lot better and less stressful to deal with. 

Diesel in Petrol Car FAQs

Misfuelling can cause significant harm to your vehicle and, in many cause, can make it inoperable, leading to it needing to be repaired. These repairs can be costly, which is why many people try to claim their insurance to help them cover the cost. 

The problem is that many insurance and breakdown cover does not include misfuelling. This is because misfuelling is considered a mismanagement issue and not strictly an unavoidable accident. 

Some will provide cover and aid after misfuelling, but this may only be available on pricier policies, and only a select few providers will include this. This means that you may have to finance and pay for the repairs yourself. 

The vast majority of misfuelling causes happen with people putting petrol in a diesel car. The nozzle is smaller and more likely to fit into a larger 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. 

Still, accidentally putting diesel in a petrol car happens a lot and causes plenty of damage to many drivers in the UK. 

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 should be something that you’re wary off 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 a massive repair fee. 

If you've put diesel into a petrol car, you'll likely need to have your vehicle drained of the wrong fuel and refilled with the right fuel. Usually, this will be done by a mechanic at a garage, although it is possible to do it yourself if you're up to the task and feel that you have enough know-how and experience. 

The easiest way to drain a fuel tank is to go underneath your car and detach the lines and small drain plug directly. Depending on how full your tank is, petrol and diesel could start to flow instantly and rapidly, so make sure that your face and eyes are covered and away from the drain and that you have a bucket to collect the excess. Draining can take a few minutes and up to an hour, and once it's empty, you'll have to flush out any excess diesel with petrol and let that flow into the bucket. Once you've done this, you should be able to put things back and restart your car. 


Because you'll need to get under your car to drain successfully, it's best to have the vehicle taken to a garage so it can be lifted. This makes the parts under the car easier to access. A mechanic will also know how much fuel to rinse the tank and have a better idea of how long to do it for. This is why it's typically best to visit a mechanic to do this for you. 

Plus, not every fuel tank can be drained directly, and more tinkering could be required to drain your car. This can make it much harder for you to do and make it more likely for you to cause issues to your car. For the best results, use a mechanic.

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