Diesel in petrol – misfuel guide

25 January 2021 | Bruce Compton

It is harder to put diesel in petrol than vice versa.  The diesel nozzle in most fuel stations is generally larger than the petrol one and won’t fit.  That being said, there are always the exceptions to the rule, and 25% of calls received by leading fuel drain specialists Auto Fuel Fix are because of diesel in petrol.

4 signs that you have misfuelled, diesel in petrol

  • Misfire
  • Car wont start
  • Loss of power
  • Thick smoke from exhaust

If you realise immediately or notice any of these signs once you start the car, turn the engine off immediately.  

What’s the damage?

If you are unfortunate enough to have made the mistake of putting diesel in your petrol car, bike or van by mistake, then take comfort in the knowledge that this rarely causes any major damage.   Diesel has to be compressed to ignite, whereas Petrol relies on the spark plugs to generate a spark.  The diesel will undoubtedly clog up your spark plugs and fuel system, hence the misfire and smoke however once drained of the wrong fuel and after having an additive added to the fuel system to clear the residual diesel, you should find that your vehicle runs just as it had before.

diesel in petrol

You could be advised to change your fuel filter and/or spark plugs at the next earliest convenience, especially if you have driven the car before realising you have misfuelled, however, these are relatively inexpensive.


Leading fuel drain specialists such as Auto fuel fix would always recommend as standard a full fuel drain after putting diesel in petrol, regardless of the quantity of wrong fuel added.

Remember…..Do not start the engine or switch off as soon as you realise.

If you realise your mishap with less than 5% of a full tank of diesel in petrol ( around 2litres or less wrong fuel), then providing you fill the tank full with the correct fuel, you should be able to drive with no repercussions and without any need to call out a specialist.

It could be advisable to use a specific additive to help cleanse the fuel system of any remaining diesel.

Long term

One point to note regarding misfuelling diesel in petrol is that some cars, bikes or vans may suffer with emission problems further down the line.  This may come to light at your next MOT.

Should you encounter any emissions problems or alike, following your fuel drain then it is advisable to consult a reputable garage or mechanic for further advise.