If you're stood next to your car right now, having pumped the wrong fuel into the tank, let's cut straight to the important advice:
DO NOT START YOUR ENGINE
If you take away one thing from this guide – the second you realise you've put the wrong fuel in your car, stop pumping and do not attempt to start your engine. We'll get into more detail later on but trying to start your car on the wrong fuel could lead to serious and costly engine damage.
I put the wrong fuel in my car, what should I do?
Hopefully, you already followed the most important advice and haven't started your car. In this case, all you'll need to do is contact your preferred breakdown service and let them know you've misfuelled your car. They'll send out a technician who can drain the offending fuel out of your vehicle and get you on the road again.
If you didn't notice the error straight away and have started your engine, then you should aim to pull over and stop the engine as soon as it's safe to do so – assuming your car hasn't already failed. At this point, call your breakdown service and have them send a technician out to help you. Some engines might be able to run for short periods on the wrong fuel type, but this will likely cause long-term engine damage if not addressed quickly.
If you've misfuelled and haven't started your engine, or your engine has already died after being misfuelled, you might need to move your stricken car to a safer location. This is best attempted with someone pushing the car and another person behind the steering wheel to guide the vehicle and press the brakes to bring it to a halt. You should only try to push your car if it's safe to do so – if not, stand away from your vehicle and moving traffic until help arrives.
What happens if you put petrol in a diesel car?
This is the most common type of misfuelling, because petrol pump nozzles are small enough to fit into diesel tank filler necks. Sadly, it's also usually a more serious problem than putting diesel in a petrol car. Diesel fuel has lubricating qualities that are essential for vital engine parts like your fuel pump and injectors.
Any petrol that makes it to these sensitive areas of a diesel engine will act as a solvent and break down this vital internal lubrication. This will quickly cause friction to build up and lead to accelerated wear on metal parts. This wear can rapidly damage or even destroy a diesel engine, leaving you with a very expensive repair bill.
If you catch yourself misfuelling your diesel car with petrol – whether you've started the engine or not – you should call your preferred breakdown service. They will send a technician to drain the offending fuel from your car's system. In some cases, you might need to replace all or part of your car's fuelling system to prevent petrol making it to your engine.
What happens if you put diesel in a petrol car?
This is rare because most diesel pump nozzles are larger than petrol tank filler necks, so they usually won't fit. It's not quite as serious as putting petrol into a diesel car, but can still cause problems for your vehicle so you shouldn't attempt to drive your petrol car if you've accidentally put diesel in it.
As covered above, diesel has lubricating qualities which means, if it gets into a petrol engine, it can coat your fuel injection system and spark plugs with residue, causing them to clog up. At best, this will impact engine performance but it could also lead to a misfire or your engine simply refusing to start if it thinks the fuel system is compromised.
Like a misfuelled diesel car, hopefully you catch your mistake before starting your petrol engine. This will make it much easier for your breakdown technician to drain the diesel from your petrol tank. If you do end up starting your petrol car with diesel fuel, stop it as soon as you realise your error, then contact your breakdown service to help drain your fuel system.
Do I still have to pay if I put the wrong fuel in my car?
It might feel like a kick to the teeth while you're already down, but you'll have to pay for any fuel you pump from a station – regardless of whether you pumped it by mistake. Most fixes for misfuelling require that your fuel tank and fuel system be completely drained, so you'll also lose the value of whatever fuel was already in there.
Think about it this way, however. Fixing a misfuelled car might mean sacrificing a tank of fuel – a valuable commodity these days – but that cost is tiny compared to the many thousands of pounds it'll take to replace a broken engine. Even if your engine's core survives, you might still be on the hook for pricey repairs or replacement parts for your fuel system – again, much more expensive than simply treating misfuelling as soon as it happens.
I have put E10 petrol in an incompatible car – what do I do?
UK fuel pumps changed from E5 to E10 petrol in September 2021 in an effort to reduce the environmental impact of road traffic. As the name suggests, this meant jumping from a petrol blend with 5% bio-ethanol to 10%.
All petrol cars built since 2011 are compatible with E10 petrol by law, but many earlier models had already been compatible for many years beforehand. It's common to find petrol cars built in the '90s that are fully compatible with E10 fuel, as it was already in wide circulation in other countries. As a result, E10 compatibility is really only an issue for very old cars or certain pre-2011 models.
Don't fret if you accidentally put a small amount of E10 in a car that isn't compatible. Broadly speaking, your engine should still work fine and is unlikely to suffer long-term consequences. Prolonged used of E10 fuel in an engine that isn't compatible can damage internal seals and lead to accelerated wear. If you do put some E10 in a car that's not compatible, consider filling the rest of the way up with E5 fuel (super-unleaded) to try to dilute the E10 as much as possible. If you put a large amount of E10 fuel in an E5 car, it might be worth calling a breakdown technician to drain your fuel tank.
What do I do if I put fuel in my AdBlue tank?
This is quite unlikely as your AdBlue filler neck is usually too small to accept a fuel pump nozzle. However, as with other errors covered here, the most important advice if you do get fuel in your AdBlue tank is not to start your car. Simply contact your breakdown service and they'll figure out what kind of flushing procedure is needed to get you back on the road.
AdBlue components including the tank, pump and injection systems aren't built to tolerate fuel – whether petrol or diesel – and will quickly fail if exposed to the wrong fluids. Avoiding starting your engine in the event you put fuel in your AdBlue system is the best way to minimise the damage from this mistake.
What do I do if I put AdBlue in my fuel tank?
This is the more common error suffered by diesel drivers, where they accidentally mix AdBlue into their standard diesel tank. If you've been paying attention so far, you've probably already guessed the most important advice, which is not to start your car if you realise you've made this mistake. Failing that, you should stop your engine as soon as you realise your error. Contact your breakdown service and let them know what's happened.
You car's fuel system, whether diesel or petrol, isn't designed to accept AdBlue. Should AdBlue fluid get into your fuel system, it can corrode metal parts and damage seals, leading to accelerated wear and probably causing a complete failure of your fuel system or engine.
Advice for avoiding refuelling mistakes
- Pay attention when filling up your vehicle
- Read the name of the fuel label at the pump to confirm it's what you're expecting
- Be aware that fuel pump colours may be different in other countries. For example, petrol pumps in the USA are black, while diesel pumps are green – the opposite to the UK's layout
- Put a reminder of your car's fuel type on the fuel filler flap or your keyring
- Some brands already do this from the factory
- Consider buying a misfuelling prevention device for your diesel car, such as a Fuel Angel
- Petrol tank filler necks are too small for a diesel nozzle so no device is necessary on petrol cars
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