What happens when you put the wrong fuel in your car?
A guide to misfuelling by Kyle Davy, Sales Manager – Fleetmaxx Solutions Ipswich
Let’s be honest – misfuelling happens more often than you might think. In fact, according to What Car?, someone in the UK puts the wrong fuel in their car every three and a half minutes. It’s one of those things that seems unthinkable until it happens to you or one of your drivers. And when it does, it’s vital to know what steps to take straight away.
Whether you’re managing a fleet or just your own vehicle, here’s my guide on how to handle it the right way — and what to avoid at all costs.
Misfuelling – Step one: Know what fuel your vehicle takes
This might sound obvious, but when you’re in a rush, driving a hire car, or swapping between vehicles in a fleet, it’s easy to make a mistake.
You’ll usually find the fuel type on the inside of the fuel flap, in the owner’s manual, or on your vehicle documents. Still unsure? Petrol engines tend to be quieter and smoother, while diesels are louder with a distinctive clatter. But if in doubt, always check with your vehicle provider or garage.
Misfuelling – Step two: Don’t start the engine
If you’ve realised your mistake before starting the engine – stop right there. Do not turn the key.
Starting the car will circulate the wrong fuel through your system and could cause significant, long-term damage. The AA advises removing the keys completely to avoid any accidental starts.
If you’ve already started the engine, switch it off as soon as it’s safe to do so and call for help.
Misfuelling – Step three: Move the car somewhere safe
If you’re still at the pump, put the car into neutral and push it to a safe spot with the help of the station staff or a colleague. The quicker you get it clear of the pumps, the better.
Misfuelling – Step four: Call your breakdown provider
Now it’s time to bring in the professionals. You’ll need a specialist to drain and flush the system properly.
At Fleetmaxx, we recommend National Breakdown, our trusted partner for roadside recovery. Their Pay-As-You-Go membership is a great option for our customers — it means you only pay when you need the service, with no monthly commitment. Ideal for business fleets and personal drivers alike.
Misfuelling FAQs
How much could it cost?
Here’s the big question: what’s the damage to your wallet?
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If you didn’t start the engine: a tank drain typically costs around £190.
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If the engine was started: you could be looking at £5,000+ in repairs to fuel pumps, injectors, or even a full engine rebuild.
Worth taking the right steps early, isn’t it?
What’s the damage based on fuel type?
Petrol in a diesel engine
This is the most common type of misfuelling – and one of the most damaging. Diesel acts as a lubricant, while petrol strips that protection away. The result? Heavy friction and potential mechanical failure. Even if you’ve only put in a small amount, we always recommend a full drain.
Diesel in a petrol engine
This mistake is less common – the diesel nozzle is usually too big to fit in a petrol tank. But if it happens, you’ll likely notice misfiring or that the car won’t start at all. Thankfully, a drain and flush should sort the issue without lasting damage.
What if you put AdBlue in your diesel fuel tank?
This is another easy mistake — the small blue AdBlue filler cap is often right next to the black diesel cap. Here’s what you should do if this happens:
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Don’t turn on the ignition or start the engine.
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The AdBlue is water-based and can cause serious damage to your fuel tank, pump, and injection system.
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Call your breakdown provider right away for a full system drain and clean.
What if you put diesel fuel in your AdBlue tank?
Thankfully, this one’s a bit harder to do – the AdBlue filler cap is smaller, and most diesel nozzles won’t fit. But if it does happen:
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Don’t start the engine or turn on the ignition.
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If fuel enters the AdBlue system and the engine is started, you might be looking at a complete replacement of the Selective Catalytic Reduction (SCR) system – and that’s not cheap.
Mistakes like this are rare, but when they happen, they can cost thousands. Catch it early and call for help immediately.
What about misfuelling E10 petrol?
Since the UK switch to E10 petrol (which contains more bioethanol), there’s been concern from drivers with older vehicles. Around 600,000 UK vehicles aren’t compatible.
If you’ve filled up with E10 by mistake, don’t panic. Add some E5 as soon as possible to dilute it, and try not to make it a regular occurrence. Repeated use could cause corrosion inside your engine over time.
How to avoid misfuelling in future?
It’s easy to be distracted — especially after a long day, an early start, or juggling a fleet of mixed-fuel vehicles.
Here’s my advice:
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Don’t trust pump colours alone – Always read the labels.
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Add a fuel type sticker to the inside of the fuel cap.
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Brief your drivers regularly if you manage a fleet.
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Use one fuel type across your fleet where possible to reduce risk.
Missfuelling our final word
If you or one of your drivers accidentally fills up with the wrong fuel — or AdBlue ends up in the wrong tank — don’t panic. Act quickly, avoid starting the engine, and call for expert help.
If you’re using Fleetmaxx Solutions for your fuel cards and breakdown recovery, rest easy — you’ve already got reliable support on your side.
Need help with PAYG recovery or want to simplify fuel management across your fleet? Give the team a call on 01367 704 910 — we’ll sort you out.
Safe driving,
