I put petrol in a diesel engine! What should I do?

Putting the wrong fuel in your car – often petrol in a diesel car – is an easy mistake to make. It is also really easy to stop your mistake from costing you thousands.

Refuelling your car is a task usually squeezed in between more important things, and while your mind wanders you may find the wrong fuel has ended up in your car's tank.

If you have put the wrong fuel in your car – either petrol in a diesel car or diesel in a petrol car – don't panic. Instead, follow these simple steps:

  • Don’t start the engine – book NRMA roadside assistance for a tow to your nearest NRMA car servicing centre or workshop 
  • If you have already started or driven the car, stop it safely as soon as you can and turn off the engine
  • Petrol in a diesel car can cause serious engine damage that’s not covered under warranty

I put the wrong fuel in my car

If you realise during or after filling up that you’ve put the wrong fuel in, don’t start the engine. Instead, call 13 11 11 for NRMA roadside assistance . Our team will arrange a tow to hopefully get you to a mechanic to drain the fuel. 

Attempting to siphon the fuel out of the tank is not recommended – you won’t be able to remove all of the fuel from the tank and could be putting your safety or the environment at risk.

If you started your car and drove away before you realised your mistake, stop somewhere safe as soon as you can and switch the engine off to minimise damage.

Diesel at petrol bowser

Putting petrol in a diesel car can cause serious damage to the fuel injection system and engine. A diesel fuel pump operates on very fine tolerance at high pressures and is lubricated by the diesel fuel.

When petrol is added to diesel it reduces its lubrication properties, which can damage the fuel pump through metal-to-metal contact and create metal particles causing significant damage to the rest of the fuel system.

Serious engine damage may also occur due to detonation caused by uncontrolled petrol ignition under the much higher compression ratio in diesel engines, also known as pre-ignition, detonation or misfire.

Related: Pros and cons of diesel and petrol

What to do if you put diesel in a petrol engine

Inadvertently putting diesel in a petrol car is more difficult to do. Diesel bowser nozzles are deliberately larger than petrol ones, so won’t fit into the filler neck of most petrol cars.

The result of putting diesel in your petrol car is not quite as catastrophic as when it’s the other way round. The car will usually run roughly and the exhaust will be smoky. But it is still much better not to drive the car no matter which type of wrong fuel you’ve put in the tank.

Damage done to your car as a result of putting in the wrong fuel is not covered under warranty, and your car insurance policy may not provide cover for the mistake either.

The NRMA motoring advice team provides professional advice for NRMA Members on a range of motoring topics, including what you should do if you’ve put the wrong fuel in your car. You can reach the team on 13 11 22 (Monday to Friday, 9.00am to 5.00pm).

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