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What to do if you put the wrong fuel in your car!

Putting the wrong fuel in a car, whether it’s diesel in a petrol model or petrol in a diesel engine, is something many motorists worry about. It only takes a moment of inattention to make the slip, and we tend to imagine that the consequences, both in financial cost and personal embarrassment, will be catastrophic. Yet, in spite of all this paranoia, we still let our thoughts wander while at the pump, only to suffer that instant of freezing horror when we realise what we’ve done.

Wrong fuel in your car?It is, perhaps, slightly comforting that approximately 150,000 people in the UK make this error every year. Although drivers of both new and used cars slip up every day, it’s more common to make a mistake when driving a new or unfamiliar vehicle, so hire cars and cars on trade plates often suffer this fate. Drivers in the motor trade are not immune to making fuelling mistakes, so there’s no need to feel as if it’s something only a bad driver would do.

Part of the reason motorists are so terrified of misfuelling is we’re not sure what, exactly, happens when the wrong fuel enters a car’s system, or what we need to do about it.

It is much more common for drivers of diesel cars to fill up with petrol than vice versa, since a petrol nozzle will fit a diesel tank, while diesel nozzles are too large for most petrol vehicles. Unfortunately, this way round also has more potential for engine damage. In a diesel engine, the fuel also acts as a lubricant, to keep things running smoothly. Petrol does not have this property, and can start to harm components as soon as it enters the system.

Most drivers notice they have used the wrong fuel while still at the pump. The damage is done when the wrong fuel begins to circulate, so it’s important to keep the engine switched off. Leave the car where it is, or push it away from the pump. If you only realise something is wrong while you are driving, pull over and stop as soon as it is safe to do so.

Many breakdown policies include misfuelling help, so if you are covered by a breakdown service, make this your first call. If you do not have cover, there are a number of companies that specialise in fuel recovery and will come out to you. This might be expensive in the short term, but could save money on repairs later, or even a new car.

A professional will drain the wrong fuel out of your tank, flush out the system, and fill up with the correct fuel, as well as offering advice on how to proceed and what to look out for.

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If you notice your mistake shortly after you start filling up, it is sometimes possible to get away with it by switching to the right fuel and brimming the tank. This is a risky strategy, however, and it is safest to call for professional help.

What can we do to prevent this potentially costly, and definitely inconvenient, error? Avoiding distraction at the petrol station is a good start. It might sound silly, but it’s easy to make a mistake when preoccupied with the journey ahead, or chatting with passengers. You should also check the label on the fuel nozzle, and, when you’ve picked the nozzle up, the indicator on the pump. Don’t rely on the colour of the hose or the position of the nozzle.

Diesel owners can buy a device which prevents a standard petrol nozzle from fitting the tank, but the simplest, and cheapest, solution is a sticker on the inside of the filler cap to remind you which fuel you need.


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