Navigating the Pitfalls of Misfuelling: What Happens When You Put Diesel in a Petrol Car

The accidental act of putting diesel in a petrol car is not just a hypothetical scenario but a reality faced by many drivers in the UK. This common mishap, misfuelling, can seriously affect your vehicle’s performance and longevity. With many diesel and petrol vehicles on the road, the risk of such errors is ever-present, highlighting the importance of professional draining services designed to correct these mistakes efficiently. This article delves into the consequences of misfuelling, exploring how diesel affects petrol engines and outlining practical solutions to address the issue.

Understanding Misfuelling Dynamics:

Misfuelling typically occurs when drivers accidentally fill a petrol car’s tank with diesel fuel. This mistake can be surprisingly easy, especially under certain conditions, such as using an unfamiliar vehicle or refuelling quickly. The design differences between diesel and petrol nozzles and filler necks can sometimes fail to prevent this error, particularly in older vehicle models or those without modern misfuelling prevention technologies.

Immediate Consequences of Diesel in a Petrol Engine:

Introducing diesel into a petrol engine can lead to several immediate problems, manifest differently based on whether the engine is started and the car is driven post-refuelling. Key issues include:

– Starting difficulties, as diesel’s thicker composition hampers its ignition in a petrol engine.

– Decreased engine performance and possible misfires, resulting from diesel’s gumming up of petrol engine injectors.

– Increased smoke emissions, a byproduct of diesel’s incomplete combustion in a petrol engine environment.

Long-Term Implications for Your Engine:

Driving a petrol car with diesel in the tank can exacerbate the situation, causing extensive damage to the engine’s fuel system. Over time, the diesel can corrode or clog the fuel injectors and spark plugs, leading to hefty repair bills. The catalytic converter, essential for reducing exhaust emissions, may also suffer, becoming blocked with soot and potentially requiring expensive replacement.

Proactive Measures to Counteract Diesel Misfuelling:

To mitigate the effects of diesel misfuelling in petrol cars, immediate and decisive action is necessary:

  1. Avoid starting the engine to prevent the contaminated fuel from circulating.
  2. Arrange for professional fuel draining services promptly. These experts specialize in removing incorrect fuel, cleaning the fuel system, and refilling the tank with the right fuel type, ensuring your vehicle suffers minimal harm.

Preventing Misfuelling Mishaps:

Adopting preventive measures is the most effective strategy to avoid the inconvenience and cost of misfuelling:

– Always verify the fuel type your vehicle requires before filling up, especially when switching between diesel and petrol cars.

– Consider installing a misfuelling prevention device that blocks diesel nozzles from fitting into a petrol car’s filler neck.

– Stay alert and focused during refuelling to avoid distractions that could lead to misfuelling.


Putting diesel in a petrol car can disrupt your vehicle’s performance and necessitate costly repairs, but understanding the issue and knowing how to respond can significantly reduce the potential damage. Preventive practices and prompt professional intervention in the event of misfuelling are key to safeguarding your engine. If you ever have mistakenly added diesel to a petrol car, remember that quick action and seeking expert help are your best solutions for resolving the issue with minimal impact.

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