Put the wrong fuel in?

Diesel in a petrol car or vice versa – what to do about a car fuel mishap

Don’t turn on the ignition or start the car – call us straight away on 0800 0727420.

AA Fuel Assist is available to Members and non-Members

If you've put the wrong fuel in, you're not alone. Putting petrol in a diesel car is especially easy, and mistakenly putting diesel into a petrol tank is also possible.

What matters most is what you do next.

Fuel price reports

Here’s what to do if you've put the wrong fuel in

1. Don't try to start the car
  • This is important - starting the car can cause permanent damage and mean costly repair work.
  • Remove the keys from the ignition instead.
2. Get to a safe location
  • Put the car in neutral.
  • If you’re still at the petrol station, get someone to help you push the car to a safe spot.
3. Call us
  • Our Fuel Assist team are on-hand to come out to you.
  • We'll drain the wrong fuel and put in the right one.
  • You'll have enough of the correct fuel to get you going.

We provide 24/7 roadside assistance.

What happens if you put petrol in a diesel car?

Putting petrol into a diesel tank causes more damage than diesel in a petrol car.

Plus, petrol nozzles can easily fit into most modern diesel filter necks. It makes it far easier to accidentally put petrol into a diesel tank than vice versa.

Petrol damages diesel engines because:

  • Diesel acts as a lubricant, helping the fuel pump to do its job.
  • Petrol does the opposite - it increases friction between parts in the diesel engine.
  • The friction isn't good news for your diesel engine.
  • The more petrol that's pumped through the diesel engine, the more damage it'll do.
  • That's why it's so important not to start the car.

Common rail (or HDi) diesel engines are particularly likely to be damaged by the wrong fuel. If there's a lot of damage, it could mean new fuel pumps, injectors, pipes, filters, fuel tank – or even a whole new engine. 

What happens if you put diesel in a petrol car?

The diesel pump nozzle is bigger than most petrol filler necks, so it doesn't really fit. That makes it far less common to put the wrong fuel in a petrol car than putting petrol in a diesel car.

Plus, it's not as bad for a petrol engine to have diesel in it so there's usually not as much damage.

Here's what happens when you put diesel in a petrol car:

  • Petrol ignites by a spark from the spark plugs.
  • Diesel in a petrol engine clogs up the spark plugs and fuel system.
  • That means the car simply won’t start.

It's a real pain. But it's not as bad as the damage that petrol can cause to a diesel engine. Your petrol engine shouldn't have any permanent damage once the fuel's drained out.

What if you put AdBlue in your fuel tank?

It can be an easy mistake to fill up your fuel tank with AdBlue. Here's what to do:

  • Don't turn on the ignition or start the engine - you’re likely to face a big repair bill if you do.
  • The AdBlue could cause expensive damage to your fuel tank, pump and injection system.
  • Please call us on 0800 072 7420 and we'll help you.

We can't remove AdBlue by the side of the road because it's corrosive. That means we may need to tow you to a local garage to fix your vehicle.

What if you put fuel in your AdBlue tank?

If you start your engine with fuel in your AdBlue tank, you might have to get the entire Selective Catalytic Reduction and AdBlue injection system replaced.

  • Don't turn on the ignition or start the engine.
  • Please call us on 0800 072 7420 and we'll help you.

How to prevent misfuelling

There are a few ways we can make it less likely to fill up with the wrong fuel:

  • Don’t rely on the colour of the hose or nozzle before filling up - look for other clues.
  • Properly read the pump’s trigger label and the fuel grade indicator.
  • Put reminders in the car, like a sticker inside the fuel cap.
  • Distractions aren't worth it, so pop your phone down and give the pumps your full attention.
  • Don't get fuel if you’re in a hurry, hungry or stressed - you're more likely to make a mistake.
  • Own a diesel? Buy a stopper to go in the filler neck so the narrower petrol nozzle can't fit.

Find out how breakdown cover can help you if you've put the wrong fuel in your car: Breakdown cover guide

Published: 29 March 2016 | Updated: 12 December 2019 | Author: The AA

Put in the wrong fuel?

Don’t turn on the ignition or start the car - call us on 0800 072 7420.

Compare breakdown cover

Learn more about choosing the right cover for you in our guide on how to compare breakdown cover. Plus, find out what’s included in breakdown cover from the AA vs RAC.

You can also discover what's included in Green Flag breakdown cover vs the AA.