What Happens When You Put Diesel in a Petrol Car?

You may think you’re the only one to make this mistake, but it is surprisingly common. But while common, it can also be costly. Putting diesel in a petrol engine car can potentially harm your vehicle, so you need to watch out. There are various ways you can limit the damage to your car and it is especially important to realise your mistake and act quickly to rectify it. Here’s what happens when diesel fuel gets into a petrol car, and what you need to do about it.

Diesel in a Petrol Car: The Consequences

So what exactly happens when people put diesel in petrol car engines? Does it damage the engine? Is it more or less serious than putting petrol in a diesel engine car? In general, the consequences of putting diesel in a petrol car are less serious than putting petrol in diesel.  There is a different method to ignite diesel fuel compared to petrol. Diesel needs to be compressed in order for the ignition to work. Petrol must be lit by a spark from the spark plugs. So when you put diesel in the wrong engine the most likely result will be it fails to start, as the diesel gets stuck in the spark plugs. You will also probably notice that the engine smokes if you try to turn it on. If it does start then the engine typically misfires. The engine may cut out if you drive it a short distance. Of course, an engine that doesn’t start is a big problem but it is potentially less serious than ruining the engine, as you can do when you put petrol in a diesel car.

What to Do If It Happens

The best thing you can do is to realise your mistake and not turn on the engine. Don’t do anything. Keep the keys out of the ignition. You will need to call a breakdown service that will drain the wrong fuel from your car before you can refill with the correct fuel and get going again.

What to Do to Prevent It

Since the nozzle of the diesel fuel pump is typically larger than the petrol filler neck, it is less likely you will make this mistake over the other way around. In order to prevent the same thing happening again in the future you can put a sticker on the fuel cap indicating the correct fuel, or use a key fob that lets you know which fuel to put in. Check the fuel pumps carefully when you are filling up. It is easy to make a mistake. It is particularly easy to make a mistake when you are driving in another country since the pumps can be the opposite way around or different colours.


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