What would happen if you put the wrong fuel in your car?

Petrol and diesel fuels have different properties such combustibility, thickness, and the engines of cars are built to handle only one fuel type. So the damage that can occur to your car depends on if the car was petrol or diesel.

Diesel has to be compressed to ignite so usually, the outcome is that the car would not start at all, since the engine is effectively clogged up. Even if it does start there is a lot of smoke and loss of power.

The damage in putting petrol in a diesel car is more pronounced, as petrol has a higher combustibility, meaning that it will detonate faster, causing misfiring and can result in permanent damage to the engine.

Design Differences Between Petrol and Diesel Fuel Systems

So putting the wrong fuel in your car can be a costly mistake. In the UK and EU, there are design differences between petrol and diesel fuel systems that are intended to prevent misfuelling. Petrol vehicles typically feature a narrower fuel tank opening, complementing the smaller nozzle found at petrol pumps. This design is intentional; it makes it physically challenging to insert a larger diesel nozzle into a petrol tank. However, the reverse scenario – inserting a petrol nozzle into a diesel tank – remains a possibility due to the smaller size of the petrol nozzle.

A Practical Solution for Avoiding Misfuelling

For individuals who own or operate multiple vehicles with different fuel requirements, the risk of misfuelling can be a genuine concern. A simple yet effective strategy to mitigate this risk involves marking the fuel tank area. Placing a clear, visible sticker or a mark indicating whether the vehicle is diesel or petrol can serve as a helpful reminder during fueling. This approach is particularly beneficial for those managing a fleet of mixed-fuel vehicles or for households with more than one type of car.

The idea behind this tip is straightforward: by marking the tank area with labels such as 'Diesel' or 'Petrol,' drivers can quickly identify the correct fuel type for their vehicle, reducing the likelihood of a costly mistake. This method is especially useful for diesel car owners, given the possibility of inadvertently using a petrol nozzle.

What should you do if you do put the wrong fuel in your car?

First of all, do not start your engine. The further the wrong type of fuel goes into your engine the more damage it can potentially do. If you have already started driving, stop in a safe place and turn off the engine.

Next arrange for the fuel to be drained. It is best to involve professionals as the drainage needs to be quite thorough, including fuel lines as well as the fuel tank.