What do I do if I’ve put the wrong type of fuel in my car?

14th Sep, 2021

Mis-fuelling your car seems like a very silly and easily-avoidable mistake – right up until the moment you make it yourself. Don’t worry though, you’re not alone. Research suggests that as many as 150,000 drivers make this mistake every year (including police officers!). In some cases, it’s even enough for drivers to end up realising: I have to scrap my car. But that doesn’t necessarily mean you’ll be one of them. If you think you’ve misfuelled your car, here’s what you need to do.

3 key things to do if you mis-fuel your car

The very first bit of universal advice is easier said than done – don’t panic. Making rash decisions out of panic or embarrassment could end up making your issue a lot, lot worse.

In short:

1. Do not drive the car

Driving the car with the wrong fuel in could cause serious or even catastrophic damage. Plus, if you knowingly drive away with the wrong fuel in your car, you run the risk of your insurer deeming the action negligent, in which case you will not be insured.

So, rather than trying to go anywhere, instead stay exactly where you are, and remove the keys from the ignition. If you’ve already started driving, stop the car and turn off the engine as soon as it’s safe to do so.

2. Get yourself to a safe area

In all likelihood, you’re already in a reasonably safe position if you’re still at the petrol station, even if other drivers may not be all that happy about it. If it’s easier and safer, put the car in neutral and get someone else to help you push it to somewhere a bit more out of the way. If you’re on the side of the road on the other hand, it’s usually best just to leave the car where it is until help arrives. Speaking of which…

3. Call for help

This isn’t an issue you can fix yourself, so you’ll need to call someone like your breakdown cover provider, RAC Fuel Patrol, or an independent mobile mechanic to come and drain your system and flush it of any errant fuel. The cost for this will probably vary, but if you’re using a mobile mechanic it’s likely to be in the region of about £250.

What happens if I’ve put petrol into a diesel car?

We’ll be honest with you – it’s probably not good news. Petrol into a diesel car generally causes more damage than putting diesel into a petrol car. It doesn’t help that petrol nozzles can easily fit into most modern diesel filter necks, so it’s particularly easy to make that momentary misjudgement. However, you can avoid the worst of the damage if you’ve realised before actually driving off.

If you’ve already made it as far as the road on the other hand, you can normally tell when you’ve misfuelled a diesel car because you may notice any of the following:

• Loud knocking while accelerating the car
• Excessive smoke billowing from the exhaust
• Sluggish acceleration
• The engine warning light illuminating
• The engine is stopping or failing to restart properly

So, what’s happening?

Essentially, your normal diesel fuel acts as a lubricant for the fuel pump, which operates on a very fine tolerance at high pressures. Petrol doesn’t have those same lubricating properties. Instead, it’ll basically act like a solvent, dissolving the lubricant and causing major friction, damaging your fuel pump through metal-to-metal contact. That can also create debris that causes further damage to the rest of your fuel system, endangering not just the pump, but also potentially your fuel injectors, pipes, filters, fuel tank and more. Wrecked fuel injectors alone can end up costing you thousands, and those kinds of figures are more than enough to write off your car.

Obviously the more petrol goes that goes through the car, the more damage it’ll do, which is just one more reason why it’s so vital that you drive the car as little as possible. Call for help, and sit tight.

What happens if I’ve put diesel into a petrol car?

It’s still not great, but the good news is that it’s not nearly as damaging as petrol into diesel. It’s also trickier to do accidentally, because diesel pump nozzle is larger than most petrol tanks, so hopefully you’d realise before you attempted to persevere. Even if you did manage to do it, the most likely case scenario is that your car simply wouldn’t start.

If you manage to get it out on the roads though, signs of a mis-fuelled petrol car include:

• Engine misfiring
• Excessive smoke billowing from the exhaust
• The engine cutting out
• The car not restarting

So, what’s happening?

Basically, the air-fuel mixture in your fuel tank ignites through a spark from the spark plugs. Mis-fuelling the car generally means that these spark plugs get coated in diesel, clogging up the fuel system. Without a proper spark, your car probably just won’t start. In the slim eventuality that mis-fuelled petrol cars do get moving, engine misfires are very common.

It’s annoying and not particularly cheap to solve, but as long as you’ve kept any movement to a minimum, you generally shouldn’t have to worry about any permanent damage to the engine once the errant fuel has been drained.

How to avoid mis-fuelling your car

Though it’s a very simple (and therefore often easy) mistake to make, you’ll be glad to hear that there are a couple of good ways to help yourself avoid making it. We’ve detailed some of the best ones below.

• Don’t rely on the colour of the hose or nozzle to differentiate between petrol and diesel. Instead, take the time to properly read the trigger label, and the fuel grade indicator
• Your car may well tell you the fuel you need – you can generally find a pointer on the inside of the fuel cap
• Give the pumps your full attention rather than using your mobile or chatting to your passengers
• Try and avoid getting fuel if you’re rushed, or stressed, or even hungry, as each of these factors mean you’re more likely to make a mistake
• If you own a diesel, it’s worth considering buying a stopper to go in the filler neck, which will stop the narrower petrol nozzle from fitting into it

Of course, the unfortunate truth is that sometimes mistakes happen. But when your car finally chugs its last – whether because it’s been mis-fuelled or simply reached the end of its natural lifespan – then you can trust us to take care of it for you right here at Scrap Car Network, and all at the very best prices. All you need to do is enter your car reg and postcode into the fields on our site, and we’ll get you an instant online quote before you can say cash for cars. It only takes a few seconds. Curious to find out how much your car is worth?