A Guide To Misfuelling

Ten years ago, there were around 1.6 million diesel cars on the roads in Britain. Today, that figure has risen to around 12 million, meaning that one in every three cars in the UK is now powered by diesel.

However, with the increased number of diesel-engine cars on the road comes the resulting increase in the number of incidents where drivers have accidentally filled their cars with the wrong fuel.

Known as misfuelling, it’s estimated that it happens around 150,000 times a year – roughly 400 times a day.

A common enough problem it may be, but that doesn’t mean it should be treated lightly. Putting the wrong fuel in your car can cause serious damage to its internal workings, leaving you to foot a bill that can range from a few hundred to several thousand pounds.

It can also be an extremely scary experience to find that the wrong fuel has been put into your car, which can potentially spell disaster for your entire engine.

To help you avoid any problems, I have put together a quick checklist of things to look out for, as well as some FAQs you might like to know.

Misfuelling checklist:

• If you’re hiring a car or driving a company car, check whether it’s petrol or diesel. Significant amounts of misfuelling incidents happen to drivers behind the wheels of borrowed cars.

• Similarly, make sure anyone who is going to drive your car knows which type of fuel it needs.

• Some diesel cars come with “Diesel only” stickers on the fuel cap. If you think you’re likely to forget, it can be worthwhile labelling your own car to avoid problems.

• Double check what the fuel pump at the petrol station says. Usually, unleaded has a green nozzle and diesel has black, but this isn’t always the case, particularly abroad. Some modern-day diesel pumps are often green to enhance the fuel suppliers´ eco-credentials, with BP being the most notable culprit.

• Always get a receipt for your fuel where possible. If you have a moment of doubt, the receipt will say which type of fuel you bought.

• Remember NOT to start your engine if you think you've filled your diesel car with unleaded. Starting the car will circulate the fuel throughout your engine,

• Seek expert help either from petrol station staff or via emergency call-out.

How does the wrong fuel type affect your engine?

Filling your car with the wrong fuel type can wreak havoc on the interior workings, with repair bills totalling hundreds of millions of pounds each year.

Putting diesel in a petrol engine will cause your engine to cut out and stop working. As diesel doesn’t ignite in the same way that petrol does, the spark plugs which ignite the fuel in your petrol engine will have no effect.

In order to get your petrol engine to start again, all the diesel fuel will have to be drained from the fuel tank and the system flushed clear to remove the oil the diesel would have left throughout your fuel system. You will most probably need to remove, clean and re-install your spark plugs and fuses if the car has been driven with diesel in the system.

Luckily, it’s usually quite hard to fill a petrol tank with diesel, as diesel fuel nozzles are specially designed to not fit in petrol cars.

However, the opposite is not true, and it can be all too easy to accidentally fill your diesel car with petrol.

Petrol will strip your diesel engine of the lubricant used to keep it ticking over and cause metal components to grate against each other, causing them to crack and disintegrate.

Along with the risk of damaging the fuel pump and injection systems, if allowed to continue, this will destroy the engine completely.

This is a "worse case" scenario, you would have to really push the car for this to happen but if the misfuel is not dealt with quickly this is the end result.

Many new diesel models feature pre-ignition systems that start the fuel pumps when the doors are unlocked.

The benefit of this is that it takes less time for the engine to warm up when you start it, but it means that the engine can be flooded with petrol simply by unlocking your doors.

How much will it cost to fix?

If you've avoided turning on the engine or stopped quickly after turning on the engine, a fuel-tank drain and system flush will 99% of the time get you back on the road immediately.

The average cost for this does depend on the car type, how far it's been driven etc. There is not a one price fits all in this industry as the fuel systems vary greatly as does the situation that vehicle is in.

Be wary of companies offering minimal call out fee's, in our experience these companies will come with a multitude of extra costs.

These can range from extra costs for draining both sides of a twin take system, or performing the system flush and the biggest one of all is a fuel system additive. We have seen these being pushed on customers for ridiculous sums of money, ranging from £300-£450!

Always check before confirming you need the service what is included and what the final price will be. The reputable companies out there will always provide this information so you aren't left with an even bigger headache.

What about breakdown cover and insurance?

Unfortunately, misfuelling isn’t covered by your car’s manufacturer and is generally also excluded from insurance policies, but there are some exceptions.

Likewise, if you’ve leased your car or it’s on contract hire, you’ll probably have to meet the cost of any repairs yourself.

What about diluting the fuel?

Technically, you can dilute contaminated fuel with the correct fuel type providing you're under 10% of the overall fuel tank capacity, but we seriously wouldn’t recommend it.

It’s usually possible on older models, however due to the fine, high-pressure diesel injection systems on modern cars this can prove a high-risk move which may end up resulting in the complete destruction of your engine.

There’s also no guarantee that mixing the correct fuel with the incorrect one will even work. It can also cause the car to run roughly for a while, and you still risk long-term component damage that’s not immediately apparent.

What can I do about it?

If you’re unfortunate enough to mix up your fuels, the best option is to identify the problem as quickly as possible, to minimise the damage by not continuing to drive and calling for expert help.

There are many companies who will attend your vehicle at the roadside and perform a full fuel drain and decontamination of the fuel system. Once this has been completed you should be fine to fill up and continue on your journey.