So you’ve got yourself a brand new car – good times. Whether it’s that new car smell or the snazzy tech that makes parking a dream compared to your previous old banger, there’s probably plenty to feel smug about. But if you’ve switched from diesel to petrol (or vice versa) in the process, there’s an important risk to be aware of: misfuelling. Putting the wrong fuel in your car, new or not, can be an expensive mistake. But catch your error early and there are some straightforward solutions. We explain what to do and whether your car insurance is likely to include misfuelling cover.
What is misfuelling?
Misfuelling is the official name for putting the wrong type of fuel in your car – so putting petrol in a diesel car or diesel in a petrol car. Neither is good news for your car, particularly if you accidentally turn the engine on before you realise. There are solutions, though, so it’s important to follow the right steps to rectify the issue.
Why is misfuelling an issue?
Diesel and petrol may come from the same source, but they are very different fuels. Your car is only designed to take one kind of fuel. Putting the wrong one in can cause major problems for your engine and other parts of the car. It’s a bigger problem if you put petrol into a diesel car than the other way round.
What happens when you put petrol into a diesel car?
Diesel is designed to lubricate engine components and diesel-powered cars rely on this lubrication to run smoothly. Using non-lubricating petrol in a diesel car has a similar effect to not putting oil in your car. The result is high levels of friction, overheating and the potential for tiny fragments of metal to come off car parts as they grind together. These can get into your fuel system and damage it, stopping the engine running. In some cases, you may even need to replace the entire fuel system and/or engine.
Even a tiny amount of petrol in a diesel car can cause problems.
What happens when you put diesel into a petrol car?
This is less serious than putting petrol in a diesel car, but it will clog up the car’s spark plugs. In a petrol car, these usually ignite the fuel, but that doesn’t work with diesel. The rest of the fuel system will then also get clogged up and the car will either cut out or not start at all. There’ll probably be plenty of smoke from the engine, though.
What should I do if I put the wrong fuel in my car?
If you haven’t started the engine:don’t! If you realise you’ve used the wrong fuel before you turn on the ignition, you’re one of the lucky ones. Starting the engine causes the most serious damage. Catch the problem before this and the effort (and cost) involved in putting things right will be much lower. Don’t even be tempted to try and drive the few metres to a parking space.
If you’ve already started the engine and started driving away (assuming your engine didn’t conk out immediately), pull over in a safe place as soon as possible and turn the car off.
Then, follow these steps:
Inform the staff at the petrol station (if possible). Even if you’ve managed to drive away, you probably won’t have got that far. They’ll probably be familiar with misfuelling (it’s surprisingly common) and may be able to offer advice or help you move your car to a safer spot on the forecourt if needs be.
Call a breakdown company. If you don’t have existing breakdown cover, you’ll need to pay a call-out fee or (in some cases) become a member on the spot – which can be expensive. Even if you already have cover, bear in mind that not all breakdown policies cover misfuelling as standard, while others offer limited cover, so you may need to pay for some recovery and repair costs. Depending on the extent of the damage and the specific breakdown provider, your car will either be sorted on the spot or towed to a garage for repairs.
If your car insurance policy covers misfuelling (see “Does my car insurance cover misfuelling?” below) and you want to make a claim, contact your insurer. If your car is pretty new, it’s worth checking your manufacturer’s warranty too.
What needs to happen to fix a car after misfuelling?
If you haven’t started the car, then there’s a good chance no damage will have been done. If so, all that needs to happen is for the fuel tank to be drained, cleaned and refilled with the correct fuel.
If you’ve started the car (and possibly driven away) then there are 2 possible outcomes:
If you haven’t driven far (or at all), you may get lucky. In some cases there won’t be any damage to your engine or fuel system. If so, you’ll just need an expert to flush the system with a cleaning agent and fill it with the right fuel.
If you’ve made it a fair distance before your car has come to a spluttering stop, unfortunately there may be more serious damage or even complete system failure. Brace yourself for some high repair charges if you need to replace the fuel system or engine.
How much does misfuelling cost to put right?
If it’s not included as part of your existing breakdown cover, you can typically expect to pay £200–£300 to flush your tank. This charge might also include a small amount of the correct fuel.
The cost of fixing more serious damage can run into thousands if you need to replace important parts of your car.
Does my car insurance cover misfuelling?
The answer is, unfortunately, often no. Research by financial analysis company Defaqto has found that only a minority of car insurance policies cover the cost of draining and cleaning a tank at the point of misfuelling. This is often specified as “misfuelling cover”. Some such policies cover it as standard, while others offer it as an optional add-on.
A higher proportion (around half), but not all, cover the cost of repairing the damage caused if you start the engine – usually under the “accidental damage” section of a policy.
Confusingly, there’s no guarantee that policies that include misfuelling cover will also include the cost of misfuelling repairs, so read your policy carefully to know what is and isn’t included.
If you can’t find an affordable car insurance policy that covers misfuelling and it’s something you’re particularly worried about, there are some specialist providers that offer dedicated misfuelling insurance.
Are there any misfuelling exclusions with car insurance?
Yes, though unlike some car insurance exclusions that apply fairly universally across all policies, misfuelling exclusions can vary significantly between insurers and policies.
Some insurers won’t cover misfuelling at all. Others will pay for repairs or replacements to damaged parts, but not draining the tank, or vice versa. Only a minority cover both. If you’re a little absent minded at the pumps or if you’ve recently switched to a new car that takes a different type of fuel, you might want to look out for a policy with full cover.
Be aware that, even if a policy covers both possible issues, it may not pay out if you’ve driven further than a specified distance using the wrong fuel.
You might think there’s no chance you’d ever put the wrong fuel in your car. But it can be surprisingly easy to grab the wrong pump if you’re distracted – especially if you’ve recently switched to a new car that takes a different fuel to your old one.
It’s often harder to misfuel a petrol car with diesel, as the nozzles for diesel pumps are bigger. This makes them harder (though not necessarily impossible) to fit into the entrance to a petrol tank. Unfortunately the same is not true of fitting smaller petrol nozzles into a diesel tank.
Tactics to reduce the risk of filling your tank with the wrong fuel include:
Use stickers, on the dashboard or the petrol cap, to remind you of the kind of fuel you need to use. This could be particularly handy if you’ve just changed cars.
Minimise distractions as much as possible while you’re refuelling. We know there’s little that can be done to block out chatter if you’ve got noisy kids in the back, but try to avoid filling up when you’re tired or stressed. And don’t attempt to multitask by checking messages on your phone.
If a fuel nozzle feels particularly tight or loose in the tank filler neck, take a second to check that you’ve picked up the right one.
If you drive a diesel car, you can buy small devices (for about £30 or £40) that prevent petrol nozzles from fitting in the filler neck.
What is E10 petrol?
E10 petrol is a new grade of petrol that replaced E5 petrol as the standard used in petrol forecourts in Great Britain from September 2021. In Northern Ireland, the change applies from early 2022.
The number after the “E” refers to the percentage of renewable ethanol in the petrol. A higher percentage reduces the greenhouse gases associated with petrol vehicles and is better for the environment. The Department for Transport (DFT) has estimated that the switch will cut transport CO2 emissions by 750,000 tonnes a year – equivalent to taking 350,000 cars off the road.
Most modern petrol cars are compatible with E10 petrol. Using it can have a tiny effect on fuel efficiency, but it’s unlikely to be noticeable in everyday driving. You can read more about the change and the reasons for it on the DFT website.
Diesel cars are unaffected by the change.
Can my car take E10 petrol?
According to the Department for Transport, 95% of petrol vehicles on the road are compatible with E10. This includes:
All new cars manufactured since 2011
Most cars and motorbikes manufactured since the late 1990s
Older, classic cars and a minority of cars manufactured before 2011 may not be compatible. You can check if your car is compatible using the DFT’s checker.
If your car is on the incompatible list (or not listed at all in the checker, in the case of some classic cars), don’t panic. Petrol labelled as “super”, “advanced” or similar on petrol pumps will continue to be E5 petrol and will remain available at many larger petrol stations, so use this instead. Unfortunately there’s no getting around the fact that this is likely to cost a bit more.
What if I put E10 petrol into a car that can’t take it?
Using a single tank of E10 petrol in an incompatible car shouldn’t be a big problem. On a one-off basis, you’ll be fine to drive and won’t need to drain the tank.
Make sure you fill up with E5 next time though, as prolonged use of E10 petrol could cause harm in an incompatible vehicle.
Bottom line
Putting the wrong fuel in your car is surprisingly easy to do, but it doesn’t have to be a disaster. Following the steps we’ve outlined can help minimise the damage (and likely costs) and get you back on the road as soon as possible. And, when you’re shopping around for car insurance or breakdown cover, add misfuelling cover to the checklist of features to look out for – it could save you a fair whack if you experience an absent-minded moment.
Frequently asked questions
Surprisingly common. The RAC estimates that about 150,000 of us make the same mistake every year in the UK.
Turn it off again as soon as you safely can. The longer you run your engine, the longer the wrong fuel will be running through your engine, potentially causing damage.
Probably not. Putting diesel into a petrol car will likely clog up the spark plugs and fuel system if you start the engine. It may stop the car from running, but it’s unlikely to cause damage to car parts. You’ll still need to get your fuel tank (and possibly the fuel system) drained and cleaned as soon as possible though. Even a small amount of petrol in a diesel car, on the other hand, can cause engine damage if you drive very far, so stop as soon as you safely can.
If you’ve put diesel into a petrol car, chances are that you’ll know straight away. The engine is likely to produce smoke and will either cut out pretty promptly or refuse to start at all. If you’ve put petrol into a diesel car, the car may well go to start with. But you may notice:
A knocking sound when you accelerate
Copious smoke from your exhaust
Slow acceleration
The engine warning light coming on
Eventually, the engine stopping all together and struggling to restart
Finder survey: Which of these is covered by your car insurance?
Response
Yorkshire and the Humber
West Midlands
Wales
South West
South East
Scotland
Northern Ireland
North West
North East
Greater London
East of England
East Midlands
Comprehensive coverage
45.88%
51.3%
51.52%
52.17%
55.63%
48.68%
54.17%
43.8%
50%
39.81%
60.92%
50%
Personal injury protection
20%
30.43%
24.24%
24.64%
21.85%
21.05%
29.17%
23.97%
19.05%
19.44%
28.74%
29.55%
Uninsured driver protection
18.82%
23.48%
16.67%
27.54%
15.23%
17.11%
25%
16.53%
21.43%
12.96%
21.84%
17.05%
Third party fire and theft
15.29%
20%
13.64%
17.39%
15.89%
15.79%
8.33%
18.18%
7.14%
15.74%
18.39%
11.36%
Misfuelling cover
8.24%
10.43%
15.15%
14.49%
9.93%
19.74%
4.17%
9.92%
11.9%
9.26%
11.49%
12.5%
Third party only
8.24%
8.7%
9.09%
7.25%
3.97%
6.58%
4.17%
11.57%
2.38%
16.67%
8.05%
10.23%
I don't have a premium car insurance
7.06%
6.09%
7.58%
10.14%
5.3%
11.84%
14.05%
4.76%
7.41%
6.9%
6.82%
None of the above
5.88%
3.48%
4.55%
2.9%
1.99%
1.32%
2.48%
2.38%
1.85%
1.15%
3.41%
Source: Finder survey by Censuswide of 1032 Brits, December 2023
*Based on data provided by Consumer Intelligence Ltd, www.consumerintelligence.com (Feb ’24). 51% of car insurance customers could save £561.39
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Ceri Stanaway is a researcher, writer and editor with more than 15 years’ experience, including a long stint at independent publisher Which?. She’s helped people find the best products and services, and avoid the pitfalls, across topics ranging from broadband to insurance. Outside of work, you can often find her sampling the fares in local cafes.
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