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Putting petrol in a diesel car or diesel in a petrol car is more common than you might think. According to the RAC, there are about 150,000 incidents of “misfuelling” in the UK every year.
Most mistakes happen when someone who normally drives a petrol car gets behind the wheel of a diesel vehicle. You might get distracted at the pumps if you’re at a garage that uses a different fuel colour code (it’s normally black for diesel and green for petrol). It’s less frequent that someone accidentally fills a petrol car with diesel as the diesel nozzles don’t tend to fit in petrol cars.
Unfortunately, misfuelling can cause thousands of pounds of damage to your car. If you realise your mistake before you drive away, you can reduce the impact on your car and the cost of putting it right.
According to Defaqto only about one in five car insurance policies include cover for misfuelling, either as standard or an optional extra.
This guide explains what you need to do in the event of misfuelling your car and what help is available.
Hopefully, you’ll realise you have put the wrong fuel in your car before you start the ignition. This is the best case scenario as keeping the engine turned off will limit the damage done to your vehicle.
Here’s what you should do if you haven’t turned on your engine:
If you have already turned on the ignition, don’t panic. Taking the right action can limit the damage done to your vehicle.
Here’s what you should do if you have turned on your engine:
There are some immediate and common signs you might experience if you’ve misfuelled your car.
Here are some signs you have put petrol in a diesel car:
Here are some indications you have put diesel in a petrol car:
Putting petrol into a diesel car is the most common form of misfuelling as the smaller petrol nozzles easily fit into diesel cars.
Misfuelling this way causes the most damage if you turn the ignition key. Illuminating the dashboard lights could mean your fuel pump kicks into life, but instead of priming the engine with diesel before it starts, your car will be sucking petrol up the fuel lines. This means they’ll need draining and flushing as well as the fuel tank.
If you actually start the engine, things will be even worse. Diesel acts as a lubricating oil, making sure the engine parts run smoothly and helping to minimise wear and tear. However, when petrol is added to diesel, the resulting mixture behaves like a solvent that dissolves the lubricant. This will increase the friction between engine parts, which can cause severe damage.
Petrol fuel in a diesel engine can also damage the catalytic converter.
Drivers are less likely to accidentally put diesel in a petrol car as the diesel fuel pump nozzle is much larger than a petrol nozzle. If you do put diesel in your petrol tank, it’s less serious than the reverse scenario.
The lubricating properties of diesel mean the fuel will coat the spark plugs and fuel system which can often lead to misfiring, smoke, and the engine either failing to start or cutting out.
If you realise you have misfuelled before putting the key in the ignition, the fuel tank will need to be drained and flushed, and can then be filled with petrol as normal.
However, if you start the engine, soot will quickly build up on the spark plugs, causing the fuel injectors to become clogged and your engine to lose power. In this situation, as well as the fuel tank needing to be drained and flushed, the fuel lines, spark plugs, fuel filter and injectors could also need inspecting. The system will need to be properly cleaned, but after that you should be able to fill with petrol as normal.
E10 petrol became the standard grade of petrol in England, Scotland and Wales in September 2021 and in Northern Ireland in November 2022. E10 petrol is blended with up to 10% renewable ethanol, making it a more environmentally-friendly fuel.
However, E10 isn’t compatible with a number of older cars. You can check if your vehicle can run on E10 online.
If you put E10 in a non-compatible car, it may still run, but if you keep using E10 some parts may become damaged over time. There’s no need to drain the tank if you fill up with E10 – just put the right fuel in as soon as possible to dilute it in your car’s system.
How much it will cost to fix your car after misfuelling depends on:
To give you a rough idea, the RAC’s Fuel Patrol costs £290.99, but existing RAC members get a £50 discount. The AA offers a similar service called AA Fuel Assist which costs £270 for AA members and £300 for non-members.
Car insurance does sometime cover misfuelling, but not always to the same extent. An insurer might:
Policies also offer varying levels of cover. These might include:
According to a 2018 study by Defaqto, only 20% of car insurance policies included misfuelling as standard, and a further 8% offered it as an optional add-on.
Here are some examples from leading insurers:
If misfuelling isn’t covered by your car insurance and there isn’t the option to add it, you can buy standalone misfuelling cover.
Most well-known car breakdown policies don’t usually cover misfuelling in their standalone policies – the RAC, AA and Green Flag all exclude it.
However, the RAC and AA both offer car breakdown members a discount on misfuelling services – RAC Fuel Patrol or AA Fuel Assist respectively. These services come to the roadside or petrol station and clean and drain your tank.
Perhaps confusingly, some car insurers offer RAC breakdown as an add-on to car insurance and this cover does include misfuelling (see Hastings Direct and Esure above).
Of the well-known car breakdown providers, AXA covers misfuelling, with cover restricted to two claims per year and a maximum value of £250 per claim. Lesser-known firms, including StartRescue.co.uk, 2Gether Insurance, Ping Insurance and Dynamo Insurance, all cover misfuelling up to £250.
Think carefully about whether you really need misfuelling cover. You’re unlikely to need it if you only drive one car and it runs on petrol, but if you swap between diesel and petrol cars or have misfuelled in the past, you may benefit from insurance.
First, check whether misfuelling is covered by your car insurance or any car insurance you plan to buy. If not, check whether it’s covered by your car breakdown cover, whether this is a standalone policy or an add-on to car insurance.
When comparing policies, consider:
Yes, any amount of petrol can cause serious damage to a diesel car.
If you spot your mistake just after starting to fill up, hang up on the pump and do not start the engine. Move your car to a safe place and call for misfuelling help.
Draining the wrong fuel from a car can take anywhere from a few minutes to a few hours depending on:
If misfuelling is covered by your car insurance and you make a claim, this could affect your future car insurance premiums.
Think carefully before making a claim. In some cases, your car insurance excess will be more expensive than simply paying for a fuel specialist to drain your tank.
