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

Putting the wrong fuel in your car can be a costly mistake, and it's one that affects around 150,000 motorists every year. But whether you’ve put petrol into a diesel car, or diesel into a petrol car, the most important thing to do is not to start the engine.

I’ve put petrol in my diesel car – what should I do?

This is the most common type of misfuelling because the petrol nozzle can fit easily into the filler neck of a diesel car's fuel tank, and it is the more serious problem.

If you’ve put petrol into a diesel car, the most important thing to do is not to start the engine. Starting the engine will allow the fuel to circulate around it, wreaking havoc on the entire system. Your fuel tank needs to be drained before you drive the car.

The petrol will act as a solvent, damaging the fuel pump and other parts of the fuel system. If left unchecked, this could mean a costly repair of your car’s fuel system, or a complete replacement of the fuel pump, diesel injectors, filters and fuel tank.

I’ve put diesel in my petrol car - what should I do?

This is a rarer problem, as most diesel fuel pumps won’t fit into a petrol filler neck. However, if you put diesel into a petrol car's fuel tank, do not start the engine because this will allow the fuel to circulate and will contaminate the fuel system.

The dangers of putting diesel into a petrol car are less serious than the other way around. Diesel is a heavier, oilier fuel than petrol and isn’t as easy to ignite in the engine of a petrol car. If the diesel is allowed to circulate around the fuel system, the engine may not start.

Again, most repairs will start with a complete flush of the fuel tank to get rid of the contaminated fuel.

How much will it cost to fix if I put the wrong fuel in my car?

This will vary depending on the type of car, the size of the engine, and whether or not you’ve started the engine.

Most recovery providers will start by draining the fuel tank completely to remove the contaminated fuel, but more repairs may be required. According to the AA, the cost of calling out one of its fuel recovery specialists is £190 if you haven't started the engine. If you have, and especially if you've driven the car, the costs could be much higher. The RAC says that in the worst-case scenario, a repair could cost as much as £5000.

You may be able to claim back the cost of repairing your car through your insurance policy, under an accidental damage clause, but this usually only applies to fully comprehensive policies.

Both the AA and the RAC, two of the UK’s biggest breakdown providers, offer bespoke misfuelling services. There are also lots of independent operators offering mis-fuelling services, so check online to see which offers the best value for money.

Should you buy a diesel car? Or would a petrol or electrified model suit you better? Our free What Fuel? tool can help you decide with four easy questions.

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