Sometimes it’s not until your vehicle breaks down on a petrol station forecourt, or it comes to a halt as you leave the pump, that you realise you’ve filled your car with the wrong fuel. Either way, it can be frustrating and often a costly experience. Motorists with multiple cars — or those who drive fleet pool cars regularly — are more likely to make this mistake.
So, what should you do if you put in the wrong fuel? And what can you do to avoid being in that situation in the first place? We’ve compiled some helpful tips to curb your frustration and save you from unnecessary costs.
Don’t turn on the ignition
Many vehicles have an electric, low-pressure pump in the fuel tank that operates the moment you turn on the ignition.
So, if you’ve just put the wrong fuel in your car and turned on the ignition, it will soon be circulating its way through the fuel system, causing potential damage in a matter of seconds.
Leaving the ignition off gives you a better chance of minimising the damage and you may need only to get the tank drained and topped up with new fuel.
Petrol into a diesel system
It’s more common for motorists to put petrol into a diesel system than the other way around and, unfortunately, it has potential to be the most damaging (aside from diesel exhaust fluid).
A vehicle’s diesel fuel pump operates on fine tolerances and it is lubricated by the viscose diesel fuel. If you run petrol through a diesel system you’ll strip the lubricant, causing the pumps to run dry and damage them from the metal-to-metal contact.
If your vehicle has a common rail (CRDi or HDi) diesel engine, then it pays to be extra careful as repairs or replacements after filling up with the wrong fuel can be expensive.
If the fuel pump is damaged, or contaminated fuel reaches the common rail system, you’ll need to pay for the fuel pumps, injectors, fuel rail, filters and tank to be cleaned out, and you might even need replacements.
The process and cost of repairs will depend on the type of vehicle and how long you’ve been running on the incorrect fuel.
In worst-case scenarios, bills can be in the thousands of dollars — especially if a large chunk of the fuel system requires replacement, and repairs to the engine are necessary.
If your vehicle is under warranty, it also pays to consult the manufacturer or the warranty company.
Diesel into a petrol system
Diesel motorists will be aware they need to unlock the pump before using it. Picking up a petrol pump without having to unlock it first should automatically trigger warning bells.
This may explain why fuelling your petrol vehicle with diesel is less common, but it still happens. Luckily, though, it generally doesn’t cause too many problems.
After putting diesel in a petrol vehicle you’ll probably find that the engine may just simply fail to start or if it does, it’ll soon splutter out afterwards.
In some cases your vehicle may continue to run but you’ll notice that it’s not running as well as usual. Typically your car will display symptoms such as pinking, exhaust smoke and a loss of power.
Different grades of petrol
If a certain grade of petrol is specified for your vehicle, for example 95 octane, and you accidently fill it with a 91 octane, there is no need to panic and drain the tank. Just fill up when you can with the recommended fuel.
Modern vehicle engine management systems are designed to constantly adapt to the conditions and the computer should adjust the engine operation to cope with the fuel. You may experience lower power output than usual until back to normal.
To avoid using the wrong fuel it pays to double check what fuel is recommended, which is often shown inside the fuel flap.
If you do use the wrong fuel, there are companies that can come to your rescue — as long as you haven’t touched the ignition. For a fee, they can siphon out the contaminated fuel from the tank.