What happens if you put petrol in a diesel car ?

Even if you don’t read any other part of this article – read this: Putting petrol in a diesel car is dangerous. Do NOT drive your car if you have done so.

You don’t need to understand the mechanics of what happens if you put petrol in a diesel car to know that it’s not a good idea. But this article is going to explain exactly why it’s bad and what to do if it happens to you.

Because this isn’t exactly a rare occurrence:

Misfuelling – as it’s known – happens to around 150 000 drivers per year in the UK. So if this has happened to you, don’t worry. You’re not alone…

Here’s what to do:

The first thing you need to know – it’s dangerous

Petrol is flammable. Very flammable. Don’t mess around with it.  This is important for your own safety – and that of innocent passers-by who haven’t put the wrong fuel in their car today!

The other danger is to your vehicle (and your wallet). Diesel vehicles aren’t designed to have petrol in their fuel injection system or engine. Thus, the damage isn’t likely to be covered by your insurance.

What to do if you put petrol in a diesel car.

1) If you haven’t yet started your vehicle – don’t

If you haven’t turned the key and started your car yet, things may not be that bad. It’s not the ideal start to your day, but it is at least manageable.

But, whatever you do, do not turn that key.

If the wrong fuel makes it through to the engine, that’s going to be a much bigger problem.


  • Get someone to give you a hand pushing your car to a safe spot away from the pumps.
  • Give your breakdown cover people a call. Hopefully, they can come out and give you a hand.
  • Consider giving your insurer a call while you’re waiting too. Telling them what’s going on can make it easier to make claims for repairs later on.
  • It’s possible that your breakdown company will be able to drain your car’s fuel tank where it is. Then you’ll be good to fuel up again properly and be on your way.
  • The alternative is that your car will need to be taken to your local garage and drained there.



Old gas station for petrol and car fuel

2) If you’ve already started driving – STOP as soon as it is safe to do so

Okay, the news here is less good.

If you’ve already started driving, you need to stop as soon as you can.

If you’ve noticed anything we might call petrol in diesel car symptoms – the vehicle juddering to a stop is the most obvious one – you definitely need to stop to be on the safe side.

You’ll want to:


  • Stop somewhere safe.
  • Turn off the vehicle.
  • Call your emergency breakdown service as soon as possible.
  • They’ll need to take your vehicle to a garage and perform a complete system flush.
  • Then they’ll need to carry out a full diagnostic of the engine management system.
  • Sadly, if repairs are needed, it’s not likely to be a small job. We’re talking potentially thousands of pounds here.
  • Calling your insurance company to see if you’re covered is probably a good idea. If the vehicle isn’t worth much, you might need to consider the scrap heap.



Why is putting petrol in a diesel car so bad?

Petrol is a solvent. Petrol-driven cars are designed to handle it. Diesel, however, is a lubricant. Diesel engines rely on the fuel lubricating some of the moving parts.

This means that diesel pump components can be damaged by petrol as there is not enough lubrication, possibly resulting in the creation of metal particles which can work serious harm on the rest of the fuel system.

Petrol can also damage a diesel engine when it combusts (a normal part of a car’s operation) as it is more volatile. This more powerful detonation (called knocking) is very dangerous.

If you haven’t yet caused the fuel to be pumped around the engine, you shouldn’t have a problem. After draining and re-filling, a tiny amount of petrol in your diesel car probably won’t make a difference.

If the petrol gets into the fuel system and engine, however, the more likely it is that you will be facing serious damage.

How to stop putting petrol in a diesel car ?

Weirdly, the situation doesn’t happen the other way very often. Probably because the standard diesel petrol pump nozzle won’t easily fit in a petrol car.

Here are some general tips to make it easier to stop putting petrol in a diesel car:

  • Try not to fill up when you’re tired, in a hurry or having a conversation with someone.
  • Try to actually concentrate on what you’re doing rather than do it on autopilot.
  • Pay attention to which car you’re driving if you have more than one or you are renting.
  • Check the brand of fuel you’re using (the same colour hose does not always mean the same fuel).
  • If you’re at a different filling station, do be aware that hose colours may also be different from those you’re used to.

But, in all honesty, the simple solution is the best solution:

If you really want to never have to worry about what happens when you petrol in a diesel car, whack a sticker on the filler cover. Then you can’t go wrong.