What happens if you put diesel in a petrol car? Effects and remedies

Published on 17 Dec, 2021, 5:06 AM IST

Updated on 6 May, 2025, 11:43 AM IST

Team Ackodrive

12 min read

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If you own a car or have basic knowledge about automobiles, you likely know that cars typically run on either petrol or diesel. Despite clear labelling at fuel stations, misfuelling remains a common error and can lead to severe damage. So, what happens if you put diesel in a petrol car, or vice versa? This article breaks down the risks, signs, and consequences of filling the wrong fuel type in your vehicle.

Contents

What Happens If You Put Diesel in a Petrol Car or Vice-Versa?

Accidentally filling your car with the wrong fuel is more common than you might think. Whether it’s due to distraction, unfamiliarity, or miscommunication, the outcome remains the same once misfuelling happens; the damage is often unavoidable.

Both petrol and diesel fuels have different properties. Hence, the working mechanism of a petrol and diesel engine is different. For instance, the petrol engine uses spark plugs to ignite the air-fuel mixture, while the diesel engine uses compression to ignite the fuel. So, whether it's petrol in a diesel car or diesel in a petrol car, it will damage the engine's internal components. The following sections will explain the consequences of misfuelling a vehicle.

What are the Consequences of Misfuelling?

The consequences are inevitable whether you fill petrol in a diesel car or vice versa. However, the magnitude of implications may differ depending on the engine type, petrol or diesel.

Below, we explain both the scenarios and their consequences:

1. Diesel in a Petrol Car

It’s difficult to end up with diesel in a petrol car. The diesel fuel dispenser nozzle generally does not fit into the petrol car’s fuel filler nozzle. However, if you somehow fill diesel in a petrol car, it may cause damage to the engine’s internal components and fuel lines.

Petrol is a thin fuel, and diesel is thick. Hence, the petrol engine is not designed to cope with the properties of diesel. If you crank a petrol engine with diesel in the fuel tank, the fuel filter may clog up because it’s not designed to handle the greasy properties of diesel.

Next, if the fuel moves further, it can clog the fuel injectors. The spark plugs may also fail due to soot build-up from the mixture of petrol and diesel.

Symptoms of Diesel Mixed with Petrol

The fuel may not reach the engine due to the clogged fuel filter.
This results in an engine misfire, which begins to stutter and stall.
You may also see a lot of white smoke from the exhaust pipe.
Ultimately, the engine will lose all its power, and you will be unable to fire it up.

2. Petrol in a Diesel Car

The probability of filling petrol in a diesel car is high as the petrol dispenser nozzle is smaller and can easily fit into a diesel fuel tank nozzle. Unfortunately, petrol in a diesel engine can cause extensive damage to the internal components.

In a diesel engine, the compression ignites the fuel. Hence, the fuel enters the internal parts of the engine. It also acts as a lubricant. So, if petrol enters the engine, the drying properties of the fuel may damage the components. The fuel injection pump, which relies on diesel lubricating properties, may not function properly.

The worst part is that it's not easy to detect the presence of petrol in a diesel car. By the time you realise, it may have caused significant damage to the engine.

Symptoms of Petrol Mixed with Diesel

As mentioned above, it’s tough to determine the presence of petrol in a diesel car.
You will likely realise the mistake when seeing black fumes from the exhaust pipe.
The unburnt fuel causes the black smoke.
The engine will then stutter and lose power.
After that, you will not be able to start the engine.

What to Do If Your Car is Filled With the Wrong Fuel?

Misfuelling is unfortunate, but it is better to know what to do and what not to do when it happens. Knowledge of proper remedial measures can help limit the damage. So, if you end up with the wrong fuel in your car, you can follow the steps mentioned below.

1. Diesel in a Petrol Car

While Filling Up the Fuel

If you realise the mistake while filling diesel in a petrol car, there’s not much to worry about.
Because if you fill diesel for less than 5% of the total tank capacity, you can fill the rest with petrol.
Since diesel easily mixes with petrol, you can continue driving, and there should not be any problem.
However, it’s better to drain the diesel from the tank and flush it with petrol to avoid fuel contamination. However, this requires towing the vehicle to a service station.

After Filling up Fuel

The situation can be controlled if you realise the mistake after filling diesel for more than 5% of the tank capacity.
All you have to do is not start the engine and call for a tow service.
Tow the vehicle to the nearest service centre and drain the fuel tank. Once done, flush the tank and fill it with petrol, and you are good to go.

After Cranking the Engine

If you have started the engine after filling diesel in a petrol car, turn off the engine immediately.
Tow the vehicle to a service centre, drain the fuel and flush the tank.
Since you also cranked the engine, the fuel lines need a thorough flush with petrol. You may also need to clean the spark plugs.
After that, you can refuel with petrol and drive without any problems.

After Driving the Car for Some Time

It is the worst of all the mentioned scenarios. First, you should immediately stop the vehicle and turn off the engine.
Call roadside assistance/tow service and transport the car to the nearest service station.
To avoid fuel contamination, get the fuel tank and fuel lines cleaned and flushed with petrol.
Additionally, you may also change the fuel filter to prevent further complications. After that, you can refuel with petrol and drive without any worries.

2. Petrol in a Diesel Car

The general remedial measures remain the same as in the above scenario. If you realise your diesel car has petrol in the tank, immediately tow the vehicle to the service station. Get the fuel tank and lines cleaned and flushed before refuelling with diesel. However, there are two scenarios you should be extremely careful about. Below are more details on the same.

If You Start the Engine

Even if you turn the ignition key on, the fuel pump may send fuel through the lines.
That means the tank and fuel lines need a thorough clean and flush.
If you start the engine, the procedure gets complicated as the wrong fuel may have damaged the engine's internal components.
Hence, the engine needs a thorough inspection.

If You Drive the Car for Some Time

It's the worst-case scenario. If you have driven a diesel car with petrol fuel, the petrol may have entered the engine's nooks and corners.
Immediately switch off the engine and call for roadside assistance/tow service.
Tow the vehicle to the nearest service centre and get help from an expert mechanic because it requires more than cleaning and flushing the fuel tank and fuel lines.
The amount of work and repair bill depends on the extent of damage to the engine components.

General Remedial Instructions for Wrong Fuelling

Here are some of the general remedial steps for wrong fuelling.

Never start the engine if you realise there is wrong fuel inside the tank. It will save you a lot of money.
Next, push the vehicle to a safe location within the premises of the fuel station.
Call the roadside assistance service and take the vehicle to the authorised service centre.
If you drive an automatic car, turning on the ignition key to shift to ‘Neutral’ can trigger the fuel pump to push fuel to the system. So, be aware of that fact.

Tips to Avoid Misfuelling

If you are cautious, you can avoid the hassle of misfuelling. Below are some tips to prevent filling your car with the wrong fuel.

Have a fuel sticker: One of the most basic and simple solutions to avoid misfuelling is to have a fuel sticker on the vehicle's fuel filler cap. The sticker will indicate whether it's a petrol or diesel car.
Check before entering the fuel station: Always check before parking your car in a fuel filling station. Make sure it's the correct fuel dispenser. Slight negligence can cost you a lot.
Get out of the car while refuelling: It's better to get out and inform the fuel station attendant about which fuel to fill. It will avoid confusion, and you will see which fuel is going inside the tank.

Frequently Asked Questions

Below are some of the most commonly asked questions about petrol in a diesel car and vice-versa.

How much diesel fuel is safe in a petrol car?

If you have filled the diesel for less than 5% of the tank’s capacity, then it’s safe. You can fill the rest of the tank with petrol and continue driving. However, it’s better that you take the help of an expert mechanic before filling up the tank with petrol.

What happens if I mix petrol and diesel in a car?

The consequences of mixing petrol and diesel vary depending on whether it’s a petrol or diesel car. If it’s a petrol car, the effects may not be serious. However, if it’s a diesel car, the extent of the damage may be significant if you have driven the vehicle after mixing the fuel.

How long can a diesel engine run on petrol?

First, you shouldn’t be running a diesel engine on petrol. However, if you do so by mistake, the car engine will run for a few minutes and then lose power. The contaminated fuel may cause severe damage to the internals of the engine.

What happens if you put petrol in a diesel engine?

Putting petrol in a diesel engine can cause severe damage. Petrol reduces diesel’s lubrication, leading to metal-on-metal contact in the fuel pump and injectors. If the engine is started, it can result in costly repairs or complete engine failure.

What happens if we put diesel in a petrol car?

Diesel in a petrol car won’t ignite properly, leading to misfiring, thick smoke, and eventually the engine stalling. Since diesel is heavier and oilier, it can also clog the fuel system, requiring a full flush.

What happens if you put petrol in a diesel car?

Petrol in a diesel car can destroy the fuel pump and injectors due to a lack of lubrication. If not caught early, it can cause engine seizure. It's best not to start the car and get the tank drained immediately.

What is the difference between a petrol engine and a diesel engine?

Diesel engines employ compression ignition, whereas petrol engines use spark plugs to ignite fuel. While petrol engines are quieter and smoother, diesel engines often give more torque and are more fuel-efficient.

Which is better: fuel or diesel?

Diesel offers better fuel efficiency and is ideal for long-distance or heavy-duty use. Petrol engines are cheaper upfront, quieter, and better suited for city driving. The choice depends on your usage and budget.

What is a diesel auto engine?

A diesel auto engine is a type of internal combustion engine that uses diesel fuel and compression ignition. It is commonly used in commercial vehicles, SUVs, and some sedans for better torque and fuel economy.

What does the car's diesel logo mean?

A car's diesel logo or badge indicates that the vehicle runs on diesel fuel. This helps drivers and fuel station attendants avoid misfuelling between diesel and petrol.

What should you do if petrol is accidentally used in a diesel engine?

Do not start the engine. Call for roadside assistance and have the fuel system drained completely. Starting the car can spread the petrol throughout the system, increasing damage and repair costs.

What should you do during a diesel filling?

Ensure the car is a diesel variant before filling. Always check the fuel cap or dashboard label. Misfuelling with petrol can cause severe engine damage, especially in modern diesel vehicles with high-pressure fuel systems.

How long will a petrol car run on diesel?

A petrol car may run for a few minutes on diesel—if it starts at all—before stalling. Running it further can cause serious engine and fuel system damage. Prompt fuel draining is essential.

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