What happens if I fill my car with the wrong fuel?

Whether petrol ends up in a diesel car or diesel goes into a petrol vehicle, misfuelling can affect your engine and fuel system. The good news is that acting quickly can often prevent serious damage.

In this guide, we explain what happens when the wrong fuel enters your tank, what to do immediately, and how to prevent it in future.

If you realise the mistake while filling up, the most important step is simple: do not start the engine.

Starting the car allows the incorrect fuel to circulate through the engine, which increases the risk of mechanical damage.

Follow these steps instead:

1.      Do not turn the ignition on.

2.      Inform the petrol station attendant immediately.

3.      Move the vehicle safely if necessary (without starting it).

4.      Arrange for the tank to be drained and flushed by a professional.

5.      Contact your insurer or roadside assistance provider if support is required.

Vehicle manufacturers such as Ford Motor Company note that running an engine with the wrong fuel can damage components in the fuel system, including pumps and injectors, which can result in costly repairs.

Taking quick action before starting the car may reduce both mechanical risk and repair costs.

Putting petrol in a diesel vehicle is generally more serious than the opposite mistake.

Diesel fuel acts as a lubricant inside parts of the fuel system. Petrol does not provide the same lubrication, which means key components may wear prematurely if the engine runs with contaminated fuel.

Potential issues include:

·       damage to the fuel pump

·       injector malfunction

·       loss of engine power

·       rough running or engine failure

Modern diesel engines use high-pressure fuel injection systems, which are particularly sensitive to fuel contamination. Automotive experts warn that even small amounts of petrol can disrupt the system if the engine is started.

If petrol enters a diesel tank but the engine has not yet been started, the problem is often resolved by draining the tank and refilling it with the correct fuel.

Diesel in a petrol engine is typically less damaging, but it can still cause significant performance issues.

Diesel fuel is thicker and does not ignite the same way petrol does. When introduced into a petrol engine, it can lead to:

·       difficulty starting the vehicle

·       excessive smoke from the exhaust

·       engine misfiring

·       clogged spark plugs

If diesel is pumped into a petrol car and the engine has not been started, the safest solution is still to drain and refill the fuel system before driving.

Continuing to drive with contaminated fuel increases the likelihood of mechanical damage.

Yes, it can.

Driving a vehicle after filling it with the wrong fuel can push the contaminated mixture through the entire fuel system. This may affect:

·       fuel injectors

·       fuel pumps

·       combustion chambers

·       catalytic converters

According to automotive repair specialists and vehicle manufacturers, repair costs may increase significantly once contaminated fuel circulates through the engine.

This is why experts consistently recommend stopping the vehicle and arranging professional assistance immediately.

Insurance coverage for misfuelling depends on your policy and the circumstances surrounding the incident.

Some insurers may provide:

·       roadside assistance

·       towing services

·       guidance on emergency procedures

It is always best to contact your insurer immediately after a misfuelling incident to understand what assistance may be available.

For businesses operating company vehicles or delivery fleets, reviewing business insurance policies is particularly important. Comprehensive business insurance can help organisations manage operational risks associated with vehicles, drivers, and unexpected incidents on the road.

Although it may seem unlikely, misfuelling occurs more frequently than many drivers realise.

Industry reports from automotive service providers indicate that misfuelling incidents occur regularly across both private vehicles and commercial fleets, often caused by:

·       driver distraction

·       unfamiliar vehicles

·       rental cars or company vehicles

·       similar pump nozzle designs

The increasing number of diesel and petrol engine variants on South African roads also contributes to the risk.

Fortunately, a few simple habits can help prevent misfuelling.

1.      Double-check the pump

Always confirm the fuel type before the nozzle enters the tank.

2.      Pay attention while filling

Avoid using your phone or becoming distracted during the refuelling process.

3.      Confirm with the attendant

If someone else is filling the vehicle, clearly state the correct fuel type.

4.      Check the fuel cap label

Most vehicles indicate the correct fuel type on the inside of the fuel flap.

5.      Be extra careful with unfamiliar vehicles

Drivers are more likely to make mistakes when driving rental cars, borrowed vehicles, or company fleet cars.

If you suspect the wrong fuel has entered your tank, assistance should be arranged before driving the vehicle.

You may need help if:

·       the engine has already been started

·       the vehicle begins running roughly

·       warning lights appear on the dashboard

·       the car stalls shortly after leaving the petrol station

In these situations, professional inspection is essential to prevent further damage.

Putting the wrong fuel in your car is stressful, but it does happen. Acting quickly can significantly reduce the risk of damage.

Remember the key rule:

Do not start the engine.

Arrange assistance, drain the contaminated fuel, and refill the tank with the correct type before driving again.

And while misfuelling may be an occasional mistake, protecting your vehicle and your finances with the right insurance cover — whether personal car insurance or business insurance for company vehicles — can provide peace of mind when unexpected incidents occur.