Skip advert
Advertisement
Tips and advice

Wrong fuel: What to do if you put petrol in your diesel car

Have you filled your car with the wrong fuel by mistake? We explain what you need to do if you accidentally put petrol in a diesel car, or vice versa

Filling your car with the wrong fuel, or ‘misfuelling’, is a surprisingly common mistake. It’s massively frustrating and can cause serious damage to your car, but if dealt with straight away it can be remedied.

If you’ve just made this very mistake – don’t panic. Estimates suggest around 150,000 people misfuel their cars every year, and garages and roadside mechanics are familiar with the procedures needed to get your car back on the road. 

adblue bottleWhat is AdBlue? Diesel exhaust fluid explained

It’s far more common to put petrol in a diesel car because the delivery nozzle on a diesel pump is wider than a petrol car's filler neck. This means it's very easy to accidentally put petrol in a diesel car, but you have to be pretty determined to do it the other way around, and the chances are that you’ll realise the mistake before you start fuelling. 

Advertisement - Article continues below

Here's our guide to what you should do, and our tips on how to avoid it happening again:

What should I do if I put the wrong fuel in my car?

It is essential that you:

  • Do not start your car – or even turn on the ignition fully
  • Call your breakdown cover provider immediately

Misfuelling your car is not the end of the world, especially if you were fortunate enough to realise your mistake quickly, and haven't tried to start your engine.

Skip advert
Advertisement
Skip advert
Advertisement - Article continues below

If you’re still at the filling station, whatever you do, do not start your car. You can turn the key just enough for the steering wheel to unlock, but turning it further will cause the fuel pump to send contaminated or incorrect fuel into the engine, causing far larger problems. Instead, find help to push the vehicle clear of the pumps to a safe place, and to stop a queue forming behind you. You should only attempt this on flat ground, and if it is safe to proceed away from moving traffic.

If you have breakdown cover, give your provider a call. They may be able to fix the problem there and then, rather than taking your car to a garage. It's worth telling your insurer what’s happened, too, as keeping them informed could make it easier to claim for repairs later, if they’re required.

Advertisement - Article continues below

In order to save your engine, the entire fuel system will need to be drained of the wrong fuel. Depending on the amount of fuel in the tank, some breakdown companies such as the AA and RAC can do this at the roadside. Otherwise, your car will have to be towed to a garage that can do the job.

Skip advert
Advertisement
Skip advert
Advertisement - Article continues below

If it’s a diesel car, the tank, fuel lines and filter will need to be drained. Following this procedure, the tank will then need to be refilled and the system primed to remove any air that could prevent the engine from running properly. It is imperative that any trace of the wrong fuel is removed entirely before the car is started.

I misfuelled my car but started the engine. What do I do now?

The above section assumes you realised your mistake immediately. If, however, you started the engine and drove away, only to come to a spluttering halt, the repair process is going to be more complex and expensive. Fuel will have made its way from the tank to deep within the car’s engine and fuel system where it can cause additional problems.

Petrol that has entered a diesel engine can cause major mechanical issues. You'll need to call your breakdown recovery provider and have the car towed to a garage for examination and repair. You may be fortunate, but it’s not unusual for a repair bill of this type to run well into four figures. Check with your insurer if you’re covered. If the car isn’t worth very much, it may write the vehicle off, since it would likely cost more to repair it than its total value.

Advertisement - Article continues below
Skip advert
Advertisement
Skip advert
Advertisement - Article continues below

If you have only pumped a very small amount of petrol into your diesel car, you may not notice any difference in how it runs. However, it's still a good idea to have the system properly drained and the fuel filter changed, as petrol is a solvent and can cause damage to diesel pump components. Petrol can also potentially damage a diesel engine during the combustion cycle because it’s more volatile than diesel.

In the rarer instance where diesel is put into a petrol vehicle, the diesel could cause damage to the spark plugs and the fuel system, among other things. However, misplacing diesel into a petrol engine may not be as troublesome as doing the opposite.

Our tips on how to avoid misfuelling in the first place

There are several common measures that you can have in place to limit the chances of misfuelling happening, the most common of which is to put a sticker on the filler cover reminding you what fuel is required. 

easy fuel

Buying a misfuelling prevention device specifically for this purpose is also a go-to option for many, and is an almost sure-fire way of stopping misfuelling. A number of products of this type are available online and from vehicle accessory shops.

Carmakers such as Ford provide a so-called ‘Easy Fuel’ system that prevents you from putting the wrong fuel in your car, so misfuelling in the future might become impossible. But it’s important to remember to consciously remind yourself what fuel is required, rather than fill up on autopilot.

Frequently asked questions about misfuelling

How much does misfuelling repair cost?

The answer to this hinges quite heavily on whether or not you started your engine. If you haven’t, the chances are that you will only need to drain the fuel tank, which could cost a few hundred pounds to fix. If the engine has been run, and the wrong fuel mixture has started to circulate around the car’s internals, you could be looking at several thousand pounds worth of repairs depending on just how many parts have been affected.

Is misfuelling covered by insurance?

It’s a common misconception that misfuelling is covered, as not all insurance providers will pay out for the cost of misfuel repairs. It’s worth checking your policy documents so you’re aware if you are covered, and if you feel that it’s something you’d rather be protected for, then you can get specific add-ons with some providers for misfuelling.

How long do misfuelling repairs take?

This will depend on how much fuel has entered the tank and how accessible the tank is. If both happen to fall in your favour, a skilled mechanic could have the job completed within a few minutes. But if a substantial amount of the wrong fuel has gone in, and the tank is located in an awkward place, it could take several hours.

Of course, this is entirely assuming that the engine hasn’t been started. In the event that it has, it’s difficult to predict how long the repairs could take given that the severity of the damage will likely range on a case-by-case basis.

How will my car tell me that I’ve misfuelled?

There will be several telltale signs, which range from excessive engine noise and a loss of power to thick smoke expulsion from the exhaust. In some cases, the car may not even start, or conversely, the engine may refuse to switch off once it’s started. These are general points, however, and may not be the exact signals that you may see if you were to misfuel.

Fed up with filling up entirely? Check out our list of the top 10 best electric cars…

Skip advert
Advertisement

Richard is a former editor of Carbuyer, as well as sister site DrivingElectric.com, and he's now Deputy Editor at Auto Express. Having spent a decade working in the automotive industry, he understands exactly what makes new car buyers tick.

Skip advert
Advertisement

Recommended

Engine management light: what to do if it comes on
Engine warning light
Tips and advice
12 Jun 2024

Engine management light: what to do if it comes on

Limp mode: common causes and how to fix it
Dashboard warnings
Tips and advice
5 Jun 2024

Limp mode: common causes and how to fix it

How to check if a car has outstanding finance
Outstanding Vehicle Finance Check
Tips and advice
20 May 2024

How to check if a car has outstanding finance

Peugeot EV customers benefit from new 8-year, 100k-mile warranty
Peugeot e-2008
News
15 May 2024

Peugeot EV customers benefit from new 8-year, 100k-mile warranty

Most Popular

Engine management light: what to do if it comes on
Engine warning light
Tips and advice
12 Jun 2024

Engine management light: what to do if it comes on

Best new car deals 2024: this week’s top car offers
Carbuyer best new car deals hero
Deals
14 Jun 2024

Best new car deals 2024: this week’s top car offers

Dartford Crossing guide: charge times, fines and how to pay
Dartford Crossing
Tips and advice
3 Jun 2024

Dartford Crossing guide: charge times, fines and how to pay

Tips & advice

View All
Car dashboard warning lights: the complete guide
Car dashboard symbols and meanings
Tips and advice
26 Mar 2024

Car dashboard warning lights: the complete guide

Electric car charging stations: a complete guide
Public EV charge point
Tips and advice
11 Jan 2023

Electric car charging stations: a complete guide

PCP vs HP – which type of car finance is right for you?
PCP vs HP
Tips and advice
17 May 2022

PCP vs HP – which type of car finance is right for you?

Average speed cameras: how do they work?
Average speed cameras: how do they work?
Tips and advice
21 Mar 2024

Average speed cameras: how do they work?

Best cars

View All
Top 10 best car interiors
Peugeot 208 hatchback
Best cars
25 Jun 2021

Top 10 best car interiors

Top 10 best electric cars 2024
Best electric cars
Best cars
16 May 2024

Top 10 best electric cars 2024

Top 10 best cheap-to-run cars 2024
The best cheap-to-run cars 2023
Best cars
2 Jan 2024

Top 10 best cheap-to-run cars 2024

The UK's top 10 fastest hot hatchbacks 2024
Fastest hot hatchbacks hero
Best cars
2 Jan 2024

The UK's top 10 fastest hot hatchbacks 2024