Luke's Car Advice: What if I put the wrong fuel in my car?

By Luke Caesar - General Manager - August 01, 2017

Luke's Car Advice: What if I put the wrong fuel in my car?

When diesel pumps were located in the far corner of the petrol station, away from gas and unleaded petrol, it was harder to make this mistake. However, you often find the petrol pump now has all 3 fuel types in a row.

There’s not much chance you’ll accidentally put gas into any vehicle except one that takes gas, as the nozzle has a unique shape.

When might I get the wrong fuel?

Unfortunately, it’s much easier to mix up petrol and diesel. And it happens at least 600 times a year, in South Australia, according to the RAA.

1. Putting petrol in a diesel car

This is the easier mistake to make as a petrol nozzle is smaller than a diesel one, so it’ll fit easily into the fuel tank opening.

The sooner you realise your mistake, the better!

If you’ve only put a tiny bit of petrol in, you may get away with it if you fill the rest of the tank with the correct diesel fuel. Opt for a higher grade (more expensive) fuel which has more lubricity to overcome the friction petrol creates inside your car.

Truck drivers actually used to add small amounts of petrol to diesel tanks in winter in Europe to help the truck start, which proves that the engine can handle it, though it’s definitely not recommended any more.

Don’t start the car!

If you’re not sure how much has gone in or it’s more than the smallest amount, then you'll need to take action to undo the mistake, before you move the car.

If you realise your mistake before you start the car, it’s not too bad. Call the RAA or get mechanical assistance right away, BEFORE starting the vehicle.

The fuel will need to be flushed from the system, and all the filters will need to be replaced. This costs around $500, depending on the car you drive.

What are the consequences of running a diesel car on petrol?

If you’ve accidentally put petrol into a diesel car, this can cause extensive damage to your car engine if you start to drive. If you start the engine, you’re going to hear unusual noises and experience abnormal engine performance.

Irregularities include uneven acceleration, misfires, and excessive smoke from the exhaust. If you’re not sure if you’ve put the wrong fuel in at this point, check your fuel receipt, or if you don’t have it, it’s going to be cheaper to call roadside assistance immediately, than to keep driving with the wrong fuel.

Major repairs will usually be needed, and these are very expensive, ranging from $4000 to $17, 000, with an average cost of $7, 000. Unfortunately, this isn’t usually covered by your insurance.

2. Putting diesel into a petrol car

This is harder to do as the fuel pump for diesel is larger and usually won’t slip into the opening in your fuel tank. It’s more likely to occur if you’re filling your car from a jerry can. This is a good reason to label your jerry cans clearly.

If it does happen, potential consequences aren’t as damaging because the engine won’t actually run.

You’ll still need to drain and flush the fuel tank, and replace the filters before you’ll be back on your road.

How to avoid the wrong fuel

Misfuelling costs Australians $10.2 million nationally each year, so how can you avoid it?

Install a diesel misfuelling prevention device

There’s a few different models available in Australia, double check before you buy that it will fit inside the fuel cap of the particular model of car that you have.

It changes the shape of the fuel opening, which prevents you from being able to insert the petrol fuel nozzle.

More tips to prevent misfuelling

If you switch cars from time to time, you’ll be at higher risk of putting the wrong fuel into the tank. Usually a diesel tank fuel flap will have a label on it to remind you.

  • Don’t rely on the colour of the pump - check the label.
  • Be sure to label your jerry cans clearly.
  • When you’ve changed cars, be extra careful at the petrol station.
  • Try not to refuel when you’re in a rush or feeling stressed.
  • If you drive a diesel car, insert a misfuelling prevention device that blocks you from inserting a narrower petrol nozzle.
  • If you’re in a hire car, or getting used to a new car, leave yourself reminders. Hopefully the different look and feel of the car is enough, but it doesn’t hurt to play it extra safe.

Hopefully you’ll never put the wrong fuel in the car, but if you ever do, remember the most important thing is that you don’t start the engine.