I put the wrong fuel in my car. What now?!

There are a few steps to take right away if you think you’ve put the wrong fuel in your car:

Step 1: Do not start your vehicle. Don’t even put your key into the ignition. Don’t even look at it.

Step 2: If you have already started driving your car, pull over and turn the engine off while regretting your life choices.

Step 3: Cancel your appointments, because you’re not going anywhere in a hurry.

Whether you’ve put petrol in your diesel tank or vice versa, your vehicle’s fuel tank will need to be fully drained and your fuel system will need to be flushed to prevent major dramas down the road. It’s not ideal for sure, but luckily there are people who can help.

What do I do if I’ve put petrol in a diesel tank?

Putting petrol into a diesel car is the easiest fuel mix-up error at the bowser, because petrol nozzles also fit into a diesel tank. Petrol in a diesel tank is also the most serious if the petrol has a chance to go through the fuel system, and (sorry to say) can quickly lead to terminal problems.

This is because petrol lacks the viscosity and lubricating properties that diesel fuel injection systems require to run. While some older diesel vehicles could tolerate a small amount of petrol in their system, modern systems don’t like it much at all. In a worst-case scenario you could be looking at replacing the engine, fuel tank, fuel pump, injectors and filters.

Basically, the further the wrong fuel goes in the system, the more expensive the fix is likely to be. The best way to avoid that? To not let it go through the system at all. Even turning the key on could prime the fuel line.

So here’s what to do when you’ve put petrol in a diesel vehicle: Call your roadside assistance, a wrong fuel service or a tow truck, and stand by.

What do I do if I've put diesel in a petrol tank?

Putting diesel into a petrol tank is usually harder to do because diesel nozzles don’t easily fit into a petrol tank. However, this mixup can and still does happen through jerry cans and other misadventures. Although diesel in a petrol tank isn’t quite as catastrophic as the other way around, it can still cause serious damage to the fuel injection system and engine if you allow that diesel to circulate in the system.

Once again, the best bet is to call your roadside assistance, look up a wrong fuel service or arrange a tow.

Who do I call when I’ve used the wrong fuel?

First, see if your roadside assistance policy will provide any cover in the case of misfuelling a car. If not, you can either call a wrong fuel service to come to you, or you can arrange for a tow to a mechanic workshop nearby. A wrong fuel service can usually come to your vehicle and handle it on the spot.

Tip: If you need to move the vehicle to a safe place while you wait, ask for someone’s help to slowly push the unstarted vehicle in neutral.

Can roadside assistance help with wrong fuel?

Misfuelling is typically excluded from most roadside assistance policies, however aspects of it might be covered on certain policies. Some might cover a tow to a mechanic, for example, but not the actual fuel system drain and flush.

If you have a roadside assistance policy it’s always worth checking with your provider, because it could save you a fair bit if they do cover anything.

How can I tell I’ve used the wrong fuel if I’m already driving?

If you’re already driving with diesel in your petrol engine, you might realise there are problems as it starts to lose power or makes a knocking sound.

Meanwhile if you’re already driving with petrol in your diesel engine, symptoms can include rough running of the engine or a concerning amount of smoke pumping out behind your car.

Surely I can just siphon the fuel out myself?

It’s really not a wise idea! Siphoning won’t be enough to completely drain the tank, and it won’t do anything to flush the wrong fuel out if it’s already in the system. Much like dentistry and legal advice, this is something that’s best left to the pros.

Luckily, there are enough people mixing up fuels that wrong fuel extraction businesses exist.

The final step when you put the wrong fuel in your car…

Is to remember that you’re not alone. Around 7,500 Aussies put the wrong fuel in their car each year, so it’s actually a fairly common mistake. Remember that it’s also easy to do when different servo brands use differing colour systems across their bowsers.

Misfuelling your car might be highly inconvenient and a little embarrassing, but hopefully with quick action it’ll be a mere blip on your memory rather than a pricey mechanic’s invoice. And if you do manage to convert your car into an expensive driveway ornament – well, at least you know where to find a great second-hand car.