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Independent, impartial advice for car buyers and car owners

Put the wrong fuel in your car? Three things to do before you panic

Whether it’s because you’re driving a car that you’ve not used, the pumps weren’t clearly marked at the petrol station or you just had a momentary lapse in concentration, putting the wrong fuel in your car is easy to do.

Unfortunately, it always seems to happen at precisely the wrong time, leaving you late for work, or that first meeting with the new in-laws, or that plane that’s leaving in an hour.  And though you can’t magically undo what you’ve done, with a bit of common sense and calm, you can prevent the wrong fuel doing more unnecessary damage to your vehicle by following these easy steps.

1. Do not turn on your engine

Occasionally you won’t realise that you’ve put the wrong fuel in your car until you’re halfway down the motorway and your engine suddenly starts to lose power.  And if that’s the case, all you can do is call a breakdown assistance service and wait for them to come to the rescue.

However if you realise that you’ve used the wrong fuel before you’ve turned the engine on, then you’re in luck and could save yourself a lot of time and money.  This is because the moment you turn the engine on the fuel is drawn up into the system, further damaging your engine.

If your car normally runs on diesel, the fuel pump will ordinarily be lubricated by the diesel in order for it to run smoothly. However the petrol will act as a solvent, removing the lubrication and causing the metal parts to grate against each other.

If you put diesel into a petrol car, the potential damage isn’t as severe but it will still cause your engine to smoke a bit and run badly, so it’s best to get the diesel out as soon as possible.

By not turning your engine on you can save yourself a lot of hassle and make the repair man’s job a lot easier.

2. Calculate how much of the wrong fuel you have put in

Is this person putting the wrong fuel in this car?Although it’s normally best to drain all of the fuel from your tank when you use the wrong fuel pump, if you realise your mistake while you’re still pumping, you may be able to get away with not calling out the repairman.

When you realise that you’ve used the wrong fuel, try to calculate how much you’ve pumped in. If it’s less than 10% of the tank capacity you should just be able to top up with the correct fuel and drive away.  However, if you’re unsure how much you’ve pumped in it’s always better to be safe than sorry and get the entire tank drained.

3. Call for assistance

Last but not least, you need to call your breakdown service to come and save the day.  Unless you’ve got some reliable mechanical skills, this job really needs a professional, so always call a reputable service to get you back on the road as fast as possible.

Although your breakdown service may be able to fix your car at the side of the road, if you’ve put a lot of the wrong fuel into your car, they may well have to transport your vehicle to a garage where they can carry out the necessary repairs more easily.

Putting the wrong fuel in your car is by no means unusual – in 2008 around 13 UK drivers an hour made the mistake – so if it happens to you, just remember to stay calm, keep your engine switched off and call the professionals.

You should also read: Premium petrol and diesel – are they worth the money?

Put petrol in a diesel car? Don't panic if you have put the wrong fuel in your car

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