Cars need fuel. Everyone knows that, but how many people know the damage that is caused when a car is filled up with the wrong fuel?

Putting the wrong fuel in a car is all too easily done. In fact an estimated 120,000 drivers choose the wrong fuel when filling up their car. Often it happens when you are driving an unfamiliar car, perhaps a hire car or one that you have borrowed. You stand at the gas pump, waiting for the tank to fill up so you can go inside and pay. Then it hits you like a sledge hammer: you realize that instead of diesel you have just filled the tank with petrol, or vice versa.

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The Worst Feeling in the World

It is a horrible, sinking feeling that is likely to get a whole lot worse when the garage hands you a massive repair bill. So what is the cost of filing up a car with the wrong fuel and how can you prevent such a catastrophic oversight from ruining your day, week, or even life?

Warning! Warning!

Many modern cars have prominent stickers on the fuel cap to warn you what fuel you need. This is also quite common on hire cars since their drivers are even more likely to get it wrong. Fuel pumps at gas stations are color coded too, usually green for unleaded and black for diesel, although don’t take this for granted, especially if you fill up at an isolated gas station in the middle of nowhere.

Major Damage to the Engine

It only takes a small amount of fuel to cause major damage to an engine. Diesel contains lubricant whereas gasoline is a solvent, so if you put gas in a diesel engine it will strip the lubricant from the moving parts. Modern diesel engines are highly tuned and metal grating on metal damages the fuel pump, which then cause further damage throughout the fuel system. If the wrong fuel travels as far as the common rail system in an HDi diesel car, a fuel injector cleaner might not be enough to repair the damage. You could end up having to replace the injectors, fuel pumps, fuel rail, filters and even the tank.

Diesel in a petrol tank is not quite as damaging. Diesel will clog up the spark plugs and cause the engine to misfire and potentially stop running, but once the contaminated fuel has been cleaned out using a special additive, the engine will soon be back to normal.

Act Swiftly

Either way, using the wrong fuel is immensely annoying and if you don’t act swiftly once you realize your mistake, it could end up costing you a lot of time and money. If you realize you have put the wrong fuel in, whatever you do, don’t start the engine. Call for assistance and let a mechanic clean the fuel system out for you.

If you do make the mistake of filling up with the wrong fuel and driving away, make sure you get several repair quotes as repair bills vary considerably depending on the make and model of car.


Cars need fuel. Everyone knows that, but how many people know the damage that is caused when a car is filled up with the...