Martynn Randall is technical editor at Haynes and has been with us for approaching 30 years. He's written more than 60 Haynes publications and has owned more than 85 cars and 60 motorbikes... so far!
It’s been a looooong day. It’s dark. Raining. Work has proved somewhat challenging. And now the fuel light’s come on in your car as you deal with jam after jam on the commute home. There’s no option but to make a weary unplanned pitstop.
You pull up to the pump, remove the fuel cap, and start to refill your car. “Hurry up hurry up,” you bemoan as the minutes pass, then notice something odd. Isn’t the pump in your hand usually a different colour? You’re fully alert now, and your stomach does a flip as you get that cold-hot-cold sweat feeling on your brow. You’ve just brimmed the car with the wrong fuel. Calamity. Anyone with lip-reading skills viewing the CCTV footage would likely blush.
So, what do you do? Well your next course of action depends on one of two things – whether or not you realised before you started the engine, or worse, after.
What to do if you haven’t started the engine
If you’ve noticed before you’ve fired up your vehicle’s engine, the first to do is – DON’T!
Then you’ll need to go into the fuel station and actually pay for the fuel you’re never going to use. While you’re in there, ask staff where you can safely push your car to on the forecourt, to free up the pump for someone less absent minded.
After that, you should call a breakdown service. Most breakdown providers offer a couple of services – they can either come out and drain the tank for you there and then, or since you’re a Haynes fan, take you and your vehicle home so you can drain the tank yourself.
Simply follow our step-by-step guide on how to drain or even replace your vehicle’s fuel tank altogether.
Every Haynes manual also contains a procedure on how to remove and replace the fuel tank, so if you already have a manual, you’re quids in. If not, why not look for your vehicle here.
What to do if you’ve started the engine
The engine will likely run fine for a short while, because it will use the fuel already in the pipes of the fuel system. One that’s depleted, your car will cough, at which point the realisation of what you’ve done might hit home.
First thing to do is find somewhere safe to pull over and switch off the engine.
Then you’ll need to call a breakdown provider and get your car taken to your local garage.
If you’ve filled your petrol car with diesel fuel, this isn’t as bad as when you do it the other way round. A petrol car filled with diesel can be easily flushed by a professional, refilled with the correct fuel and you should be on your way.
However, if you filled your diesel car with petrol and have run it to the point where the engine starts to cough, you’re facing a big bill.
This is because in modern system, the fuel pump is lubricated by the diesel itself, so when that diesel is replaced by petrol, which has no such lubricant in it, the pump gets damaged very quickly. And if you don’t stop immediately, the worn swarf from the pump internals can cause further damage to the engine. This is going to entail a sheepish call to your insurance provider and an increase in next year’s premium.
What if it isn’t your fault?
There have been a few cases where drivers have filled up with the wrong fuel because the pipes between the underground petrol station tanks and the pumps have been connected incorrectly.
In this case, any petrol station provider should simply agree to pay for the cost of repairs, but just in case, you need to keep a note of any credit card transaction, keep the receipt, and get a bill for the damage.
