What Happens When You Put Diesel In Your Petrol Car?

Your petrol car was just filled up with diesel, what now? How dangerous is it for your car to have diesel in it?
Sherryn de Vos
2017-02-27
Firstly, it is important to know that, if possible, you should try and avoid mixing diesel into petrol engines at all costs. It usually turns out to be a very costly mistake that can be avoided really easily. Filling up with diesel can damage your engine. We look at the reasons why it will damage your engine, the consequences of mixing and, ultimately, what to do if it has happened to you.

The Difference Between Diesel And Petrol Engines

Let’s start at the beginning and discuss what the differences are between both engines. To understand what impact it will have on your engine, it is important to know how the two engines work. Firstly, petrol engines have spark plugs. When the car is started, these spark and ignite the evaporated fuel that mixes with the air inside the engine. This is, essentially, how an engine runs, with a series of mini explosions. A diesel engine does not have spark plugs, and rather works off a piston that compresses the diesel so much that heat is generated and it catches fire.
CLICK BELOW to read about whether you should use the 93 or 95 version of unleaded petrol.
You have to keep in mind that diesel is heavier than petrol. Petrol is light so that it can evaporate easily and cause the sparks. Diesel’s weight can spread around a petrol engine and land up clogging it. We take a closer look below at what can happen.

What Happens To Your Engine When You Input The Wrong Fuel

When diesel is put into a petrol engine, the diesel does not evaporate like petrol does and there will be no spark. If you do get your car started with diesel in the tank, there is obviously still petrol in the car and you have simply mixed the two. If this happens, your car might run for a few kilometres and then cut out. Be aware, though, even without starting the car, it can clog the fuel filter and ruin all of the fuel injectors. If you do start the car, the diesel will land up filling the cylinder bores and causing a hydraulic lock. This can, in turn, cause damage to your conrods and crankshaft. For the non-mechanics reading this, this is a vital element to your engine. It will also leak into the sump, which will result in your oil being affected. Translated into English, although this will probably not destroy your engine completely, it will have a serious impact on the car.

How To Fix The Mistake

  • Do not start your car. Starting the car will result in the diesel being pumped all over the engine, which you need to avoid. It will be easier to remedy the situation if the engine has not ignited.
  • Have your car towed to your closest mechanic. This is if the petrol attendants don't know what to do.
  • Empty the tank completely and try flushing with clean petrol.
  • If your car is fuel injected, you will need to unhook all of the fuel lines at the injector connection. Run fuel through them until only petrol comes out.
  • Refill your tank with petrol, start it and run it for a while. Hopefully, you will soon have only petrol running through the car’s veins.
  • Don’t forget to do an oil change too after it is put in. Diesel will also leak into the cylinders. You will need to make sure that these are properly flushed out before starting your car.