Fuel mix-up: what should you do?

A fuel mix-up is one of the most common causes of breakdowns requiring the intervention of a breakdown service. It is often due to a distraction, a habit picked up with another vehicle, or not knowing which fuel to use (e.g. in a rental car).

What should you do if you've put in the wrong fuel?

While filling up:

• Stop filling up as soon as you notice your mistake.
• Avoid starting your engine!
• If you need to move the vehicle, push it manually.
• Notify the person in charge of the petrol station, who can drain the tank, or call your breakdown service.

On the road, just after leaving the petrol station…

You realise your fuel mistake just after setting off again, or you notice your engine is making a strange noise, or 'coughing'?

• Park your vehicle as quickly as possible somewhere you can stop safely.
• Turn off the engine. Continuing to drive would only make the situation worse and damage your engine.
• Put on your high-visibility vest.
• Call your breakdown service.

While driving:

Your vehicle's engine is behaving strangely and cuts out while driving? Most of the time, this breakdown will occur at most a few kilometres after leaving the petrol station.

• Switch on your hazard lights.
• Try to bring the vehicle to a stop in a safe spot along the road and turn off the engine.
• Do not try to restart it, put on your high-visibility vest and contact your breakdown service.

In every case, it is necessary to call for assistance. If the mistake is spotted quickly, before your engine is damaged, the repair will be fairly quick and will only cost you the price of draining the tank and labour. If the damage is more serious, however, repair costs can run into several hundred euros, or even more!

Thanks to your technical assistance contract, you can call on a professional breakdown mechanic who will come to you quickly to fix the problem on the spot or tow you to a garage where the repair can be carried out. However, fuel and repair costs remain your responsibility.

The international naming of fuels

On 12 October 2018, a new naming system came into force across the whole European Union.
The new labels are as follows:
Diesel ⇒ B7
98 octane petrol ⇒ E5
95 octane petrol ⇒ E10

Petrol + diesel = a dangerous mix

The most common mistake is adding petrol to a diesel tank. If this mix exceeds 10%, it risks seriously damaging your engine. The reason is simple: diesel lubricates the parts of the injection pump, whereas petrol does not have this function and will quickly destroy the protective film of the injection system.
Aside from the risk of damaging your engine, a petrol + diesel mix is highly flammable and increases the risk of explosion.

Since it's easy to insert the nozzle of a petrol pump (unleaded or premium) into a diesel car's tank, this is the most common mistake.
The opposite is, in principle, not possible, since the opening of the tank on petrol vehicles has a smaller diameter than the diesel nozzle.

Did you know?
Diesel = "gazole" or "gasoil" in France and "gasóleo" in Spain.
In Spain, "gasolina" = petrol (leaded or unleaded)… Don't get caught out! \

E85 biofuel

E85 fuel, known as bioethanol or superethanol, is a plant-based fuel that is increasingly sold in certain countries, including France. It is made up of 15% petrol and 85% bioethanol. Only fill your vehicle's tank with this type of fuel if you have a "flexfuel" car designed to run on bioethanol.
Very few cars can use this fuel.
So don't be tempted, even though its price is noticeably cheaper than traditional fuels. You risk seriously damaging your engine!

Fuel mix-up: what are the risks?

Using the wrong fuel can cause significant engine damage.
For example, if you put diesel in a petrol car, it can damage the injectors and the fuel pump.
Correcting a fuel mix-up can be costly. It may require draining the fuel tank, cleaning the fuel supply system and, in the worst cases, replacing damaged parts.
In some situations, using the wrong fuel can increase the risk of fire, especially if the vehicle is forced to run on it.

Good to know: even if the vehicle manages to run on the wrong fuel, there can be a significant drop in performance, misfiring, loss of power or excessive fuel consumption.

AdBlue: keep a close eye on it

AdBlue is a solution made mainly of demineralised water and high-purity urea (32.5%) used in diesel vehicles to reduce nitrogen oxide (NOx) emissions produced by the engine. This solution is injected into the exhaust system, where it breaks down into ammonia and carbon dioxide. The ammonia then reacts with the NOx on a specific catalyst to convert them into nitrogen and water, both of which are harmless to the environment.
In Euro 6 type vehicles, which are generally more recent models compliant with Euro 6 emissions standards, using AdBlue is crucial to meet strict regulatory pollution requirements. If the AdBlue tank is empty, the vehicle may reduce its performance to limit polluting emissions, or in some cases, it may not even start.
It is therefore important for diesel vehicle owners to regularly check their AdBlue levels and refill as needed to ensure the emissions reduction system works properly and to avoid performance and engine start-up issues.

How can you avoid putting in the wrong fuel?

• Double-check the fuel before using it
• Stick a label showing the fuel type next to your tank
• Be especially careful when filling up at a petrol station (or buying a fuel brand) you don't know. Don't rely on the colour of the nozzle.
• Be particularly attentive if you're driving a car you're using for the first time (e.g. a rental car). Check with the rental company before setting off about which type of fuel to use (as well as how to open the tank!).

Read also: "Where can you find the cheapest fuel?" and "Requesting technical assistance from Redion"

First published: 06/2016 - Updated: 06/2024

Article written in collaboration with We are the words.