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

Every three and a half minutes, someone in the UK puts the wrong fuel in their car. It seems like a silly mistake that’s easily avoided, but apparently not, so here’s what to do if (when?) that happens to you.

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15 Sep 2023

What happens when you put the wrong fuel in your car?


Filling up your car with fuel can be something all car owners do frequently, but that doesn’t mean we don’t still make mistakes. In fact, according to the RAC, 150,000 put the wrong fuel in their car in the UK every year.

If this does happen to you, don’t panic. The first rule after putting the wrong fuel in a car is don’t turn on the ignition. The most serious damage from misfuelling happens after turning on the ignition.

Putting petrol in a diesel car

Diesel cars work by using fuel as a lubrication oil. This ensures the engine parts run smoothly to prevent wear and tear. When petrol is put into a diesel vehicle, the mixture acts like a solvent, ultimately dissolving the lubricant. If you then switch on your ignition after putting petrol in a diesel car, it will circulate the mixture and increase friction between the components, thus damaging parts of your car, including fuel lines and pumps.

Once petrol has been put in a diesel car, repairs can be expensive, as your entire fuel system will need to be replaced. Some car insurance policies cover misfuelling, which is something to check with your insurer.

Putting diesel in a petrol car

Putting diesel in a petrol car is less of a worry than putting petrol in a diesel car.

If you have put diesel in a petrol car and have already started the ignition, the diesel will likely coat your spark plugs and the fuel system, which will often lead to misfiring. Your engine may then give off smoke, cut out, or fail to start at all.

To fix this issue, you should drain the fuel system as soon as possible.

Misfuelling symptoms


If you are unaware of putting the wrong fuel in your car, there will be symptoms to look out for, where your car will tell you that something is wrong.

If you have put petrol in a diesel car, symptoms may include:

  • The engine stops altogether
  • Your car struggling to restart
  • A loud knocking sound when accelerating
  • The engine warning light is illuminated
  • The car’s acceleration is slower than usual
  • Excessive smoke coming from the exhaust


If you have put diesel in a petrol car, symptoms may include:


  • The engine misfiring
  • The engine cutting out
  • The engine fails to restart
  • Excessive smoke coming from the exhaust

What if I started my engine?


If you have started your engine after filling up with the wrong fuel in a car, don’t panic. If it is safe to do so, turn off your engine immediately, or if not, pull over to a safe spot first. Put the vehicle in neutral and call a professional to come and drain, and then flush your fuel system.

Misfuelling can happen to anyone, so it is important to ensure that this is part of your breakdown cover. At Asda Money, our breakdown cover offers fast roadside assistance  when you put the wrong fuel in your car, where a professional will take your car to a nearby garage, to get it back on the roads again.

How much does it cost to fix a misfuelled car?

The cost of fixing a misfuelled car depends on whether the car is petrol or diesel. Petrol cars deal far better with taking the wrong fuel than diesel cars do, so if you own a diesel car, the cost is likely to be far higher than if you owned a petrol car.

The cost is also dependent on your car insurance or breakdown cover, as being able to claim for putting the wrong fuel in your car can save you some money overall.

If you aren’t covered for misfuelling, the average cost to get your fuel drained ranges from £400 to £800. This is in addition to any repairs needed for the damage the wrong fuel may have caused to the car’s fuel system.

Top Misfuelled FAQs:


What happens if I put the wrong fuel in my car?

The most important thing to do if you have realised you’ve put the wrong fuel in your car is to not turn on the ignition. However, if you have already turned on the ignition if your car is petrol and you have inserted diesel, your engine will either not start, smoke, or cut out.

If your car is diesel and you have inserted petrol, the car will show various symptoms, such as excessive exhaust smoke and the engine stopping altogether, and the entire fuel system may need to be replaced.


What happens if you put petrol in a diesel car and drive it?

If you put petrol in a diesel car, the engine may struggle to restart or may cut out altogether while driving. Excessive smoke may also come from the exhaust, and you may notice the acceleration is much slower than usual. If driven, petrol will also damage the car’s fuel system, so this may have to be replaced.


How long will a car run with the wrong fuel?

Although it is possible to drive a car briefly with mixed fuels, it should be avoided. If the car does start, the distance the car will go will depend on the ratio of wrong fuel to right fuel that is in the tank.


Can you claim on insurance for the wrong fuel?

Whether you can use your car insurance to claim for misfuelling is determined by what add-ons you have included in your policy. Misfuelling is sometimes an add-on option, such as a key cover or windscreen cover. Misfuelling can also be included if you have breakdown cover added to your car insurance.


ASDA Money is a trading name of Asda Financial Services Ltd and Asda Stores Ltd which for Breakdown Cover are Introducer Appointed Representatives of Liverpool Victoria Insurance Company Limited.

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