Put the wrong fuel in your car?

Petrol in diesel car or vice versa – what to do about a car misfuel

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 a common mistake, and putting diesel into a petrol tank is also possible.

What matters most is what you do next.

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

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.


Why you should choose us for breakdown cover

  • Our Patrols will usually get to you in less than an hour and get you back on the road around 30 minutes after arrival
  • We fix 4 out of 5 cars at the roadside
  • We’re a Which? recommended breakdown cover provider for the sixth year running in 2023
  • UK drivers have consistently rated us as the best breakdown service against all other major breakdown providers

Verify the above at theaa.com/best.

Wrong fuel in car symptoms

Putting the wrong fuel in your car and starting up the engine can lead to some pretty nasty symptoms, such as:

  • Your engine starts making lots of unusual noises
  • Your car starts shaking, shuddering and jumping while you’re moving
  • Your car starts spewing lots of smoke from the exhaust pipe
  • You get an engine misfire

What to do if you've already started the engine with the wrong fuel in your car

Even if you only realise you’ve put the wrong fuel in your car after you’ve already started it, you can minimise the damage caused by stopping and turning off your car as soon as possible. Park somewhere safe and call us to get your fuel removed and the correct fuel added.

Having started the engine with the wrong fuel, your car may be badly damaged, so it’s not guaranteed that you’ll be able to drive away after a fuel switch without needing further repairs.

Can the wrong fuel damage the engine?

Yes, putting the wrong fuel in your car can damage the engine, but moreso if you start the engine. A misfuel is also worse when a diesel vehicle receives petrol. This is because petrol creates friction in a diesel engine when what it really needs is lubrication. The more you drive a diesel car with petrol fuel, the worse the damage gets.

What happens if you put petrol in a diesel car?

Putting petrol in a diesel car 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.

How long does it take to remove the wrong fuel from a car?

The length of time required to drain the wrong fuel from your car can vary based on the model and type of fuel system/engine. It can also depend on how the fault is reported. If you’re sure you put the wrong fuel in your car, then AA fuel assist will come straight to you. If you’re unsure whether you have the correct fuel, this may take longer as we’ll need to diagnose the problem.

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

Can you put petrol in a diesel car?

It’s possible to put petrol fuel into a diesel car, as the petrol pump may fit your filler cap, however, you shouldn’t ever put the wrong fuel in your car as this can cause permanent damage.

How much of the wrong fuel can you put in your car?

Even if you’ve only accidentally poured a few drops of the wrong fuel into your car, it’s best not to risk driving. Make sure to get your car checked over by a professional mechanic.

Will 5 litres of petrol damage a diesel engine?

Yes, 5 litres of petrol in a diesel engine is more than enough to cause catastrophic damage if left long enough, and particularly if you start the engine. Make sure to call us right away for fuel assistance on 0808 120 9663.

Does insurance cover putting the wrong fuel in my car?

Some insurers do cover misfuelling, but it’s best to check with your own provider.

Published: 29 March 2016 | Updated: 21 July 2023 | Author: The AA

Put in the wrong fuel?

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

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