Wrong fuel in your car? Here’s what to do

You’ve no doubt heard that the wrong fuel in your car engine can be a disaster. But it can be an easy mistake to make and happens more than you might think. So what can you do about it?

If you’re stood at the petrol station and think you may have put the wrong fuel in your car, the most important thing to do is stop. And don't turn on your ignition. If you're already on the road, find a safe place to pull over and turn off your engine.

In this article, we’ll take you through what you need to do next, what the wrong fuel can do to your car’s engine, and how to prevent misfuelling from happening.

First steps in the event of misfuelling

Misfuelling is defined as putting anything other than the specific fuel designed for your car into its engine. Most commonly, misfuelling covers putting either petrol into a diesel tank or diesel into a petrol tank.

Regardless of the type of engine or the fuel used, your first steps would largely be the same:

1. Don’t turn on the engine. If you need to move the car, pop it into neutral and ask someone to help you get it to a safe location.
2. If you’re already on the road, find somewhere safe to pull over and switch off your car. The less time the wrong fuel spends circulating in your engine as you drive, the better.
3. Make arrangements to drain the incorrect fuel from your engine, either by yourself or with professional help. Your insurer may also be able to arrange an approved expert to come and assist you.
4. Don't let the wrong fuel sit in your car for any longer than necessary. Even if you haven’t yet turned on the ignition, the incorrect fuel can still slowly damage your engine.

What happens if you put the wrong fuel in a car?

If you’ve put diesel into a petrol engine

Of the two most common forms of misfuelling, putting diesel into a petrol car is probably the least destructive, especially if you managed to notice before starting your car up.

Petrol engines are combustion engines; spark plugs ignite the petrol fuel (which is mixed with air) to get the engine’s pistons pumping and your car going. To do this efficiently, petrol is more flammable than diesel as well as thinner in consistency.

The thicker nature of diesel means that a petrol car’s fuel pump will have a hard time moving the mix through the system, especially through the fuel filter. As a result, you can expect your spark plugs, fuel filter, and fuel injectors to clog up, eventually causing the engine to seize. The extra heat and pressure created by the diesel fuel can also go on to damage the catalytic converter, a vital and expensive car component which helps to filter exhaust emissions.

Your next question will likely be, how much does it cost to fix damage caused by the wrong fuel in a car engine? It's hard to give a clear estimate but, for example, replacing the catalytic converter can cost up to £1,000 alone.

If you’ve put petrol into a diesel engine

In general, diesel engines are at greater risk for costly damage if topped up with the incorrect fuel.

Petrol is a solvent that will dissolve the lubrication provided by diesel and other oils within your engine. This extra friction can impact the whole fuel system from fuel pumps to pipe injectors, and the added heat created can also damage the catalytic converter.

All in all, you could find that putting petrol in your diesel car could go so far as to necessitate a replacement fuel tank or even a whole new engine if worst comes to worst. This could cost you anything from £500 to £5,000 for a full engine replacement and installation.

How to know if you put the wrong fuel in your car

Symptoms of the wrong fuel having been added to your tank include:

• An engine that refuses to start at all
• An engine that is misfiring, cutting out, and eventually failing to start
• An unusually large amount of smoke coming from your exhaust, often black
• Sluggish acceleration
• An illuminated engine warning light
• A loud knocking sound as you accelerate
• Your engine seizing

If you notice any of the above after pulling away from the petrol station, you may have put in the incorrect fuel. Be sure to stop and take a closer look.

What about E10 fuel?

As part of a concerted effort to reduce carbon emissions, E10 fuel replaced standard grade (95 octane) petrol across the UK in 2022. E10 fuel contains renewable ethanol and is manufactured in a way that is more eco-friendly.

According to Gov.uk, 95% of petrol-powered vehicles on the road today can use E10 fuel and all cars built after 2011 are E10 compatible. In the event you mistakenly misfuel with E10 in a vehicle that is not compatible, however, simply top up with regular E5 to dilute the E10 in your car’s system. For full information and recommendations on E10 fuel visit the Gov.uk website.

Draining the incorrect fuel from your car

When it comes to how to remove the wrong fuel from your tank, depending on when you realise the mistake and how handy you are, you may actually be able to drain that fuel yourself.

Some fuel tanks have a drain plug at the bottom of the fuel tank, allowing easy and direct access to getting rid of the incorrect fuel. If not, you could consider siphoning out the offending fuel or making use of a manual pump to get it all out, before replacing it with the correct fuel.

Alternatively a professional fuel drain service may be your best option. Widely available in the UK, these mobile services can come directly to where you are with specialist equipment that will carefully and effectively get rid of the contaminated fuel for you. You can expect costs of between £50 to £250 (depending on your location) for this service, with additional fees charged depending on the scope of any damage caused.

The process of draining the car’s fuel tank can take anything from a few minutes to a few hours. This time frame will hinge on whether your car has a sealed tank, how accessible the tank is, and how much of the incorrect fuel has been added.

Steps to prevent misfuelling

Fuelling nozzles are sometimes interchangeable, and often petrol can be found right next to the diesel pump. This means that if you’re distracted when filling up, you may not immediately notice if you’ve used the wrong fuel. Unfortunately, if your car runs for any length of time with this incorrect fuel circulating, you could end up with permanent damage to your engine that can be costly to repair.

The best thing you can do to prevent misfuelling is to pay attention as you top your car up. Don’t pick up your phone or chat to a friend. And make sure you double check the pump’s trigger label and the fuel grade injector before you pump.

Finally, if you’ve recently changed cars and the type of fuel you need, a bright sticker reminder inside the fuel cap can prompt you to double check the pump. In addition, if yours is a diesel car, you could consider installing an attachment that will stop you being able to insert the narrower petrol nozzle into your car in the first place.

Key takeaways

Most importantly, if you misfuel and want to know what to do if you start your car with the wrong fuel, the best thing you can do is to simply stop, safely, and pull over. Mistakes happen and the sooner you realise a misfuelling error, the better. In the best case scenario, you may only be looking at needing to have your tank drained.

However, while knowing that the incorrect fuel in your car doesn’t immediately signal disaster, it’s still worth taking every precaution you can to prevent it from happening. The reality is that misfuelling can severely damage your car, require costly repairs, and may not be covered by your insurance. So if you are uncertain about exactly what you are covered for, be sure to examine the fine print on your car’s insurance policy.

Remember that the team at Howden are on hand at all times for comprehensive insurance that you can rely on. Contact us today.

 Also read:

• Diesel vs petrol: What’s the difference?
• How much is a car service?
• Car insurance mythbusting!
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