Putting the wrong fuel in your car – often petrol in a diesel car – is an easy mistake to make. 

If you realise during or after filling up that you’ve put the wrong fuel in, don’t start the engine. Instead, have the car towed to a qualified mechanic to have the fuel drained from the tank.

Attempting to siphon the fuel out of the tank on your own may work but is not recommended reason being you won’t be able to remove all of the fuel from the tank, and you could be putting your safety or the environment at risk.

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

Putting petrol in a diesel car can cause serious damage to the fuel injection system and the 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 the lubrication properties, which can damage the fuel pump through metal-to-metal contact, and create metal particles which can cause 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.

What to do if you put diesel in a petrol engine

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

Also, 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(if yours is a new car), and the insurance policy may not provide cover for the mistake either.

Source: NRMA