What happens when you put petrol in a diesel car?
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An honest mistake at the petrol bowser can cost you thousands of dollars in repairs, but it doesn’t have to. Here’s what to do when you put petrol in a diesel car.
Putting petrol in a diesel car can spell the start of stressful and expensive repairs to your vehicle, but it doesn’t have to.
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While there are no statistics for Australia, British comparison site GoCompare claims one in five people have admitted to mistakenly putting the wrong fuel in their car.
As we covered in our “Do diesel engines have spark plugs?” article, the fundamentals of a diesel vehicle are different from those of a petrol-powered car, meaning the engine won’t run if you put diesel in a petrol car or petrol in a diesel car.
If you have made the mistake, don’t panic – read this article first!
What happens when you try to run a diesel engine on petrol?
Many different components can suddenly fail in your vehicle if you try to run a diesel engine on petrol fuel.
Diesel has lubricating properties due to its viscosity and its flash point (the temperature at which it releases vapour and evaporates), which is much higher than petrol’s.
The fuel pump will likely be the first thing to break on your diesel vehicle if you try to run it on petrol. Diesel fuel pumps run at a higher pressure and much closer tolerances, so the diesel lubricates them when it passes through.
However, once you remove the lubrication, the chances of your fuel pump failing dramatically increase. Not only will the fuel pump fail, but it can also send metal fragments through the fuelling system, causing a blockage in the lines, filter, and injectors.
If the fuel reaches your engine, it will cause even more issues due to petrol’s lack of lubricating properties. Added stress and heat will be applied to the pistons, possibly even melting the internals.
Uncontrolled detonation of the fuel can also occur, causing melted pistons and making your vehicle run very poorly before coming to a stop. The best-case scenario for repairs would be an engine rebuild, but you can likely expect that the fuel system and entire engine will need to be replaced.
What to do when you put petrol in a diesel car
Do not start the vehicle
When you realise the mistake, the first thing you should do is stop pumping the petrol, and you should never start the vehicle.
If you have realised while pumping the fuel then you have gotten lucky, essentially all you have done is put petrol in the tank and nothing else.
You should notify the station staff so they understand why you are not moving your vehicle from the bowser.
Call roadside assistance or a wrong fuel support business
After realising your mistake of putting petrol in a diesel vehicle, you should call your roadside assistance provider or contact a wrong fuel or misfuelling support business.
They will either call a tow truck to take the vehicle to a diesel specialist, or some businesses will conduct the repair there if you have not attempted to start your vehicle.
They will pump the fuel out of the filler neck or drain it from the tank plug, replace the fuel filters, prime the diesel fuel lines, and send you on your way.
If you have started your vehicle, unfortunately, there is not much you can do on the spot. You will need to have your vehicle towed to a diesel specialist to have it inspected, and the cost figured out.
How much does it cost if you put the wrong fuel in your car?
The cost varies depending on what service you are provided, where you are located, and whether or not your started your car while the wrong fuel was in your tank.
Typically, a wrong fuel service will cost anywhere from $200 to $500 to pump the fuel out, dispose of it, fit a new fuel filter and send you on your way.
Keep in mind that you will still have to pay for the wrong fuel you put in your car and for filling the tank with the correct fuel.
If you run your vehicle on petrol, you may be lucky and only need to pay for a new fuel pump, filter, and drainage of the old fuel. You can expect a bill of up to $1000 for parts and labour.
But if you have damaged your engine, then you will likely be in the realm of $6000 to $10,000, depending on the car.
Does insurance cover putting petrol in a diesel car?
Insurance will not typically cover you for putting the wrong fuel in your car and damaging the engine. Furthermore, your warranty will be voided if you do this.
Most websites say that insurance companies “may not cover wrong fuelling.” However, we could not find a single insurance policy in Australia that covers misfuelling.
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