Wrong Fuel & Misfuelling
Petrol in Diesel
What happens if you put petrol in a diesel car?
CheckFuelPrices Editorial
Expert Written • 4 industry sources
Putting petrol in a diesel car is a serious misfuelling mistake that can cause significant engine damage. Petrol acts as a solvent in a diesel system, stripping the lubrication that the fuel pump relies on and potentially destroying it within minutes of the engine running.
Why Petrol Damages a Diesel Engine
Loss of lubrication:
Diesel fuel lubricates the high-pressure fuel pump as it flows through. Petrol has no lubricating properties, so it causes metal-on-metal contact inside the pump, rapidly wearing components.
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Contamination spreads quickly:
Once the engine is started, the contaminated fuel circulates through the injectors, fuel lines, and pump within seconds, dramatically increasing repair costs.
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Modern diesels are most at risk:
Common rail direct injection engines, found in most modern diesel cars, operate at extremely high pressures and are especially vulnerable to petrol contamination.
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What You Should Do Immediately
Do not start the engine:
If you realise the mistake at the pump, do not turn the ignition on. Even switching the ignition to the accessory position can begin circulating contaminated fuel.
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Stay in neutral and call for recovery:
Push the car to a safe area if possible and call your breakdown provider immediately. A professional drain and flush is the only safe fix.
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Tell the forecourt staff:
Inform the petrol station so they can make the forecourt safe. Do not attempt to drive the car to a garage under any circumstances.
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What the Repair Involves
Drain and flush:
A specialist will drain the tank, flush the fuel system, and refill with clean diesel. If the engine was not started, this is often sufficient.
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Pump and injector replacement:
If the engine was run on contaminated fuel, the high-pressure fuel pump and injectors may need to be replaced — a repair that can cost £1,000 to over £8,000 depending on the vehicle.
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Insurance may not cover it:
Many standard car insurance policies do not cover misfuelling damage. Check your policy, as some breakdown providers offer dedicated fuel assist cover.
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How to Avoid Misfuelling
Diesel nozzles are larger:
Diesel pump nozzles are designed to be wider than petrol filler necks, which is meant to prevent misfuelling — but it does not make it impossible, especially on older vehicles.
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Misfuel prevention devices:
After-market misfuel prevention caps fit inside the filler neck and only accept the correct-sized nozzle, offering a practical safeguard if you regularly switch between vehicles.
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Around 150,000 cases per year in the UK:
Misfuelling is far more common than most drivers realise, with roughly 150,000 incidents reported annually in the UK — most involving petrol being put into diesel cars.
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Sources
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