What do I do if I put petrol in a diesel engine?

The range of fuels on sale at the local service station can be bewildering. It’s no surprise, then, that misfuelling is common.

Diesel pumps often have extra latches on them and the fuel filler nozzle itself should give you a clue.

But it's still possible to pour petrol into a diesel tank (or vice versa), as Yan Van De Velde, the founder of Wrong Fuel Rescue, explains.

"There's usually a combination of reasons for someone to make the simple mistake of putting wrong fuel in their car," Van De Velde told carsales.

"Rushing, tiredness, unfamiliarity of a vehicle – especially if it's a work car – and distractions at the pump tend to be the most common reasons behind the mix-ups.

"The most common case, accounting for 90 per cent of mix-ups, is people putting petrol into a diesel car as the petrol nozzle fits into the fuel filler neck. The nozzle for diesel won't normally fit in a petrol car, making this less common."

Each year, Van De Velde's company deals with "thousands of motorists" who have misfuelled their car.

The cost, across the country, adds up to millions of dollars, but the cost of the wasted fuel is miniscule, compared with the cost of replacing the engine and fuel delivery system.

Services such as Wrong Fuel Rescue can send a mechanic to your vehicle's location and drain and flush the fuel delivery system.

According to the company, the process takes an hour or less.

"If you do realise you've put the wrong fuel in the tank, don't start your car. If you've already started driving, stop as soon as it is safe," Van De Velde said.

“The further the wrong fuel moves along your fuel system, the increased potential for a more expensive repair bill.

"Statistics show men are actually the worst offenders for misfuelling, making up for around 80 per cent of the rescues they attend every day," he added.

Left to work its way through the car's fuel delivery system and into the engine, incorrect fuel can cause a lot of damage which can be expensive to repair.

Furthermore, that expense won't be covered by factory or extended warranties. So the onus for meeting the cost of repairs rests entirely on the shoulders of the vehicle owner.

Filling the tank of a petrol car with diesel is not as serious as the reverse – pouring petrol into a diesel tank. Both will have some immediate impact on the car, but petrol in a diesel engine has to be sorted at the earliest opportunity.

Provided you've caught the mistake while the vehicle is still at the pump on the service station forecourt, don't turn on the engine.

Don't even switch on the ignition, as most cars are fitted with electric fuel pumps, which begin priming the fuel lines without the engine running.

Petrol is a solvent and can have an almost immediate effect on engine and fuel delivery parts that require lubrication provided by diesel fuel.

If diesel has been introduced to a petrol car's fuel tank and fuel delivery system, it will coat the engine's spark plugs and prevent the engine from firing. If the engine does start, it will run roughly and emit clouds of smoke.

In either case, ask for help pushing the vehicle to a parking space and call for a mechanic or a team like Wrong Fuel Rescue to attend and fix the problem.

If you put the wrong fuel in your car:
• Don’t panic.
• Don’t turn on the engine; don’t even switch on the ignition.
• Ask for help to safely push the car to a parking space.
• Call for a mechanic or specialist team like Wrong Fuel Rescue (1300 28 28 20).
• Also check with your roadside assist provider, if you have one – they may be able to make an assessment on-site and organise to have your car towed to a specialist.
• It’s better to get an expert to siphon fuel out of the car rather than do it yourself; modern fuel tanks are not generally fitted with drain plugs.
• If you’ve already driven off, still seek help as it may still be possible to fix by the roadside.

Wrong Fuel Rescue offers these tips to reduce the chance of misfuelling your car:
• Different brands of service stations use different colours of nozzle for the respective fuel types. Take care when switching brands.
• Be mindful when you’ve taken the family’s second car instead of the vehicle you usually drive.
• Don’t be distracted by small talk with passengers or other service station customers when filling the tank.
• You may be running late for an appointment, but don’t allow that worry to affect your focus when filling the tank.