What to do if you put petrol in your diesel car

Last updated December 06, 2021

If you have accidently put the wrong fuel in your car, the first thing you should do is nothing! Don’t start your car or even put your key in the ignition. It will be much easier to resolve the problem if the incorrect fuel hasn’t left your fuel tank and entered the cars fuel system.

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What steps should I follow if I’ve put the wrong fuel in my car?

If you’ve put the incorrect fuel in your vehicle, you should follow the steps below:

  1. In the best-case scenario, you will recognise that you have made the mistake before driving away from the petrol station. If this is the case, you should immediately alert the staff.
  2. You should move your car out of the way of other customers, so you aren’t blocking a pump. This should be done with the engine off by putting the car in neutral if it’s an automatic or out of gear if it is manual and pushing the car to a safe place.
  3. If you have breakdown cover, you should contact your provider who will send somebody to assist you at your current location. If you haven’t, you could call any breakdown provider who will send somebody out for a fee. If you haven’t turned the car on, they should be able to simply drain the incorrect fuel from your fuel tank, fill your car with the correct fuel and get you back on the road.

What happens if you put petrol in a diesel car?

Misfuelling happens more often than you would think – according to Risk Management Partners it happens every 3 minutes across the UK, with 150,000 motorists filling their tanks with the wrong fuel every year. However, it is more common for diesel drivers to put petrol in their cars, due to the size of the fuel tank neck. The nozzle for diesel won’t fit in most petrol vehicles, but diesel cars don’t have the same safety mechanism in place.

If not dealt with immediately, putting petrol in a diesel car can damage the fuel pump. In diesel cars, the fuel pump uses diesel for lubrication and if petrol enters this stream it can act as a solvent, which reduces the lubrication and quickly causes damage to the pump as there will be friction between the metal components. Other parts of the fuel system that aren’t compatible with petrol may also be damaged in the process.

As soon as you switch on the ignition after filling a car with incorrect fuel, the petrol and diesel will begin combining. This means the sooner you are made aware of the problem, the less damage is likely to occur.

What are the signs of putting the wrong fuel in your car?

If you haven’t realised and have begun driving with the wrong fuel in your car, the first sign you may notice is the car beginning to jump suddenly. Upon accelerating you may notice that the car either jumps forwards or backwards as the petrol sticks to the pistons, which causes damage to the pumps and corrodes the lubrication. This will cause metal on metal friction and cause considerable damage to your engine if not drained quickly.

Another noticeable sign that you’ve put the wrong fuel in your car is excess smoke coming from your exhaust. This is caused by the petrol and diesel heating together to warmer than usual temperatures and burning the exhaust. If you drive with the incorrect fuel for even a short period of time, there could be irreparable damage to your exhaust system.

The final sign that you have put the incorrect fuel in your car is the engine misfiring, which may cause loud bangs or splutters as you’re driving. This is also caused by the pistons struggling to operate without the lubricant from the diesel.

If you notice any of the above signs, you should immediately pull over where safe to do so, turn off your engine and call a breakdown company to offer roadside assistance.

How to avoid misfuelling

The easiest way to avoid misfuelling is to ensure you pay close attention when filling up your vehicle. You should always double check you’re putting in the correct fuel before pressing the nozzle and starting to fill your car.

If you own a petrol vehicle it will have a smaller tank neck which will mean the diesel pump won’t fit to refuel your car. This makes it impossible for you to use the incorrect fuel.

Unfortunately for diesel drivers, the tank neck is larger than the petrol pump, meaning you can easily fill your car with petrol if you’re not paying attention. However, you can have a device fitted to your car to prevent a petrol fuel nozzle from fitting into your fuel tank neck. There are various available for around £20-40, and you should make sure that they’re compatible with your vehicle before purchasing.

If misfuelling is something you have done before, this could be a small price to pay for the peace of mind that you won’t make the potentially costly mistake again.