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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 072 7420
AA Fuel Assist is available to Members and non-Members

Whether it’s down to a brief lapse in concentration or force of habit following a recent vehicle switch, misfuels happen.

Putting petrol in a diesel car is especially easy – and mistakenly putting diesel into a petrol tank is also possible. What matters most, is how you respond.

Here’s what to do

  • Remove the keys from the ignition: do not attempt to start the car. Doing so can cause permanent damage and require costly repair work.
  • Get to a safe location: put the car in neutral and if you’re still at the petrol station, get someone to push the car to a safe spot.
  • Call us: our Fuel Assist team are on-hand to come out to you, drain the wrong fuel and fill with the right one.


What happens when petrol is put in a diesel car

Petrol nozzles can easily fit into most modern diesel filter necks. This makes it far easier to make the mistake of putting petrol into a diesel tank, than vice versa. More importantly, putting petrol into a diesel tank causes more damage.

That’s because diesel acts as a lubricant, helping the fuel pump to do its job. Petrol, on the other hand, causes the reverse to happen: it actually increases friction between parts in the diesel engine. And that’s never good news for an engine. So the more petrol that gets pumped through your diesel fuel system, the more damage it will do.

Common rail (or HDi) diesel engines are particularly susceptible to damage from misfuelling. If the damage is extensive, you could be looking at new fuel pumps, injectors, pipes, filters, fuel tank – or even a whole new replacement engine. Not good.

Wrong fuel advice

What happens when diesel is put in a petrol car

The diesel pump nozzle is physically larger than most petrol filler necks, making it a far less common occurrence than petrol being put in a diesel car. Plus, the consequences of putting diesel in a petrol engine are generally not as severe.

Diesel and petrol are ignited by two completely different methods. Diesel has to be compressed to ignite. Petrol, on the other hand, is ignited by a spark generated by the spark plugs. When diesel is put inside a petrol engine, the most common result is that it clogs up the spark plugs and fuel system — meaning the car simply won’t start. 

A real pain. But all in all, not as serious as the permanent diesel engine damage that petrol can cause.

What to do if you put AdBlue in your fuel tank:

Don't turn on the ignition or start the engine - you’re likely to face a big repair bill if you do. Putting AdBlue directly into the wrong tank could cause expensive damage to your fuel tank, pump and injection system.

Please call us on 0800 887766 and we'll help you.

We can't remove AdBlue by the side of the road because of its corrosive effect, so we may need to tow you to a local garage to fix your vehicle.

What to do if you put fuel in your AdBlue tank:

Don't turn on the ignition or start the engine. If you do start your engine, you might have to get the entire Selective Catalytic Reduction and AdBlue injection system replaced.

Please call us on 0800 887766 and we'll help you.

How to prevent misfuelling

The best way to avoid misfuelling? Well the obvious answer to that is: always fill your tank with the right fuel. 

But then, that’s easier said than done isn’t it (hence, this article existing).

While no one’s perfect and it’s impossible to avoid innocent mistakes from time to time, there are a few things we can bear in mind to reduce the risk of falling foul to mishaps at the pumps:

  • Don’t just rely on the colour of the hose or nozzle before filling up. Properly read the pump’s trigger label and the fuel grade indicator.
  • If you’ve just bought a new car with a different fuel engine to your previous car, leave yourself reminders or prompts in the car to minimise the risk of you reaching for the wrong pump.
  • When you pull into a petrol station, cut out distractions and focus. For the sake of the minute or two it takes to refuel, put your phone away and give your undivided attention to the task in hand. 
  • Avoid refuelling when you’re in a hurry, hungry or stressed. When our minds are somewhere else, we’re more likely to slip up.
  • If you drive a diesel car and are worried about misfuelling, you can buy a device that fits into your filler neck to prevent you inserting the narrower petrol nozzle.

Put in the wrong fuel?

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