20 Litres of Petrol in a Diesel Car – What Happens?
If you’ve accidentally put 20 litres of petrol in a diesel car, the most important thing to do is:
Do not start the engine.
Starting the engine allows petrol to circulate through the diesel fuel system, which can increase the risk of damage to important components such as the fuel pump and injectors.
If the engine has not been started, the situation is usually much easier to resolve.
First things first – Do NOT start the car
Is 20 Litres of Petrol in a Diesel Car Serious?
Yes, 20 litres of petrol in a diesel car is a significant amount.
Even though some drivers think topping the tank up with diesel will solve the problem, modern diesel engines are very sensitive to petrol contamination.
Petrol reduces the lubrication diesel fuel normally provides. This can affect parts such as:
- the high-pressure fuel pump
- fuel injectors
- the fuel system
- filters and seals
Because of this, it’s generally safest not to drive the vehicle.
What If You Haven’t Started the Engine?
If you’ve added 20 litres of petrol but haven’t started the engine, that’s good news.
In many cases the problem can be resolved by:
- draining the contaminated fuel
- flushing the fuel system if needed
- refilling the tank with the correct diesel fuel
Because the petrol hasn’t circulated through the system yet, the risk of damage is much lower.
What If You Started the Car?
If the engine was started after adding 20 litres of petrol, the petrol may already have circulated through the system.
This can increase the risk of damage to:
- fuel injectors
- pumps
- fuel lines
The vehicle may still run for a short time, but problems often appear later such as:
- rough running
- stalling
- warning lights
- engine damage
Stopping the vehicle as soon as possible can help limit further damage.
Can You Dilute 20 Litres of Petrol With Diesel?
Some drivers consider filling the tank completely with diesel to dilute the petrol.
While older diesel engines were sometimes more tolerant, modern diesel engines are far less forgiving.
Even diluted petrol can still reduce lubrication in the fuel system, which is why driving the vehicle is generally not recommended.
Common Situations Where This Happens
Putting 20 litres of petrol in a diesel car usually happens when:
- drivers switch from a petrol car to a diesel car
- using a hire car
- driving a work vehicle
- using an unfamiliar petrol station
- selecting the wrong pump by mistake
Misfuelling happens more often than people realise.
Signs Petrol Has Been Put in a Diesel Car
If petrol has been added to a diesel vehicle, you might notice:
- difficulty starting
- engine misfiring
- loss of power
- unusual engine noise
- warning lights
These symptoms may appear once the contaminated fuel reaches the engine.
What Should You Do Next?
If you realise you’ve put 20 litres of petrol in a diesel car, follow these steps:
- Do not start the engine
- If the engine has started, switch it off immediately
- Do not attempt to drive the vehicle
- Call us for professional advice
Acting quickly can often prevent serious engine damage.
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