Mis-fuelling your car can be a horrible mistake, and the fact that it is so simple and silly almost adds injury to the insult. However, what’s even worse is the fact that the consequences of mis-fuelling can be disastrous for your vehicle.


Mis-fuelling is easy enough to do, especially if you’ve just gotten a new car, changing from petrol to diesel, or vice versa, or if you regularly switch between petrol and diesel vehicles. All it takes is it to absent-mindedly pick up the wrong nozzle on the forecourt and next thing you know you’ve done something which can potentially cause significant damage to your car’s engine.

Diesel may have some hidden costs with it when running your car.

Diesel may have some hidden costs with it when running your car.

The most common mistake that occurs in reference to mis-fuelling is filling up a diesel car with petrol. The other way around doesn’t often occur, due to the fact that the nozzles on diesel pumps are larger than the filter necks of most modern petrol cars; thus making mis-fuelling in this way practically very difficult and hard to do accidentally.

Filling a Diesel Car with Petrol

In a diesel car, the fuel itself contains a lubricant, which lubricates the engine and helps it run effectively. As soon as petrol is introduced into the diesel, it acts as a solvent, effectively nullifying the lubricant and it starts working against the engine. Without a good lubricant, metal to metal contact occurs in the high pressure pump in the engine, this erodes the components and leads to metal particles being knocked loose into the engine.

Once the engine has been damaged, and particles have been knocked loose, it won’t function properly and you won’t be able to get your car running properly. The engine can seize and it will need repairing. Petrol can also cause pre-ignition in the engine, causing significant engine damage.

Don’t Turn on the Engine

Whatever you do, it is imperative that you don’t turn on your engine. The damage from mis-fuelling can be significant, but once you turn on the engine, the mixed fuel begins to circulate around the car spreading the damage further and causing more serious erosion throughout the engine.

Petrol costs are slowly rising in price.

Petrol costs are slowly rising in price

The Hidden Costs

First and foremost, you will need to call out a mis-fuelling specialist to deal with the issue at hand. This will cost you so that they can come and drain your engine of all the mixed fuel. They can even then replace the fuel drained with the correct fuel to ensure you have enough to get you on your way.

However, the service fees for a mis-fuelling specialist is not the main cost which you will incur.

After the mis-fuelling issue has been dealt with, you will need to deal with the consequential damage that has been done to your engine. This is where things get unpleasant; if the incorrect fuel has circulated, the engine can be completely shot and significantly damaged. This will require very extensive repairs and can cost a considerable amount of money.

In fact, it is quite common that the damage done to the engine is so extensive and irreparable that it is cheaper to replace the entire engine than attempt the repairs.


The biggest costs from mis-fuelling come from the necessary repairs which need to be performed afterwards. Therefore, it is always advisable to try and reduce the damage done to your engine as much as possible. The best way to ensure this is to not turn on the engine, and to contact a mis-fuelling specialist as soon as you have realised your mistake. They can then drain the incorrect fuel before any real damage is done.

(Image credits: EEPaul and images_of_money)