How Worried Should You Be? Petrol in a Diesel Car in Edinburgh
Far less than you likely are, if it has not been started. Everyone around Edinburgh begins with "have I ruined it?", and the honest answer is usually no: petrol resting inside that tank of any diesel remains harmless until priming, cranking or driving draws it into the system. To leave the vehicle that way, ring Petrol in Diesel then leave your motor switched off. Further down, this page sets out what petrol really does inside a diesel, how far it might have got, and how to stop it happening to you a second time.
What petrol in a diesel does to the engine
Diesel does two tasks on its way through an engine. Before it ignites, it lubricates — and then it combusts. The high-pressure fuel pump and the fuel injectors are built to very fine clearances, and the diesel passing through them is what keeps those surfaces from wearing down against one another.
The second job petrol does not do at all, and the first it does badly. It is runnier than diesel and strips away the protection the system hinges on, so a pump running on a petrol mix is a pump wearing itself. And petrol is designed to resist igniting under compression, which is the reverse of what a diesel needs from its fuel. That's where the knocking comes from.
Put these together and the shape of the trouble is clear. Not contact but circulation is what causes the harm. A tank with petrol in it is a fuel fault. Whatever a worn pump sheds goes on, borne by your fuel, into the injectors further along, which is why a pump that has been working on that petrol is where a mechanical fault begins.
Edinburgh, petrol in a diesel: four cases, from mild to serious
Filled up, not once started. The best case there can be. Being on a forecourt is what makes this the case: elsewhere, the vehicle has been driven there to begin with. With the petrol held inside that tank alone, it's cleared and rinsed right where it stands, and nothing more is needed.
Ignition on, or started for a moment. With your system primed, your lines and filter now contain petrol that came from your tank. Usually little more than emptying, purging and seeing to your filter, and so still simple.
Driven a few miles. Now the pump has spent these miles labouring on weakened fuel. Miles is only half of it; how hard it was driven counts just as much. Either way this work runs to your tank, the lines, your filter and fresh fuel through the whole system. Driving the children to the local primary school is one kind of trip. Getting as far as Dunfermline, under 15 miles away, makes a very different job — as does any distance on the M8, under 10 miles from Edinburgh, with your engine labouring hard all the way.
Driven on until it protested — clattering, smoke, an uneven idle, a soft throttle. What you are hearing is the engine signalling fuel that no longer behaves like diesel. Pull up wherever you are — the verge on North Bridge, a lay-by, a side street — and leave the vehicle there. Lasting damage is very unusual when a car is stopped soon, and the fuel drain and flush that still go first deal with it.
Stories Edinburgh people hear about petrol in a diesel
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Nothing is removed when you top up — that tank simply holds more of the same mixture. The assumption behind that advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
Myth: "A current diesel can cope with a bit of petrol." If anything, the reverse. More precise components and higher pressure are how a modern diesel runs its fuel, and that makes the protection matter more, not less.
The myth that catches drivers off guard: if it starts and drives, it must be unharmed. The driver of a petrol motor fed diesel normally stops, because it will not run, and the damage stops there. A diesel fed petrol usually starts, idles and drives away as if nothing has happened, whilst your pump wears. Fine and running aren't the same thing.
An outdated workaround for a distinct issue lies behind this one. Myth: "Add some two-stroke oil and drive the car home." What petrol has thinned remains weakened, and the petrol remains in your tank anyway.
Myth: "Drain your tank yourself and you are sorted." After your engine has been run, some of the petrol is no longer in your tank: it is in the filter and the fuel lines, and it goes right back through your pump on the next start. On top of that, petrol emptied into a can by the road is genuinely dangerous.
Petrol in a diesel: how does it take place?
On purpose? Never. Through carelessness? Seldom, if ever. One way only, since of the nozzles: the slimmer petrol one slips inside a diesel filler with almost no resistance, while the diesel one mostly won't fit a petrol motor. That's how the forecourt makes it easy.
The moment habit stops matching the car is the moment it occurs. Hire cars, courtesy cars, and motors that are new to you. Households running one of each, petrol and diesel. A forecourt you know, but with its pumps arranged differently. Filling up in a rush on the way to Edinburgh Waverley, with a train to catch. The first fill-up in a diesel Volkswagen Golf after years of driving petrol is exactly the moment it occurs. The hand repeats what it has always done once you add rain, a phone call or a back seat full of children.
Next time you fill up in Edinburgh: avoiding petrol in a diesel
- The label is what counts, and so read the petrol pump instead of the colour: in the UK unleaded handles are usually green and diesel black, yet not on every forecourt.
- In a car you don't know, look inside the flap over your filler or at the cap before your first fill: many vehicles state the fuel type there.
- Mark the key. In a house with one of each, a coloured fob or a sticker on the diesel's key does more than any amount of meaning to remember.
- It sounds silly and it does the trick: on your first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the petrol pump.
- Whilst you're thinking about something else, this is an easy mistake to make — so tuck your phone away.
- Up to a point, a misfuel inhibitor helps: some diesels have a filler designed to block a petrol nozzle, and aftermarket devices are available for the remainder. Treat it as a backstop, then keep checking the pump.
- Stop the moment you realise. Less petrol inside the tank makes a weaker mix. It doesn't change what to do next, which is still not to start it.
Petrol already in a diesel around Edinburgh? Begin here
The order of things is short, then. Leave it unstarted, with the ignition switched off too. Yet at the forecourt, at BP or anywhere else? Ask the staff to help you roll the car away from the pump. Next, 0333 366 0103. We'll ask what got in, about how much, and if it has been run.
Corrosion and deposits form the issue with AdBlue, where petrol means lost protection. So if it was AdBlue, say so — and read its own Edinburgh page.
One petrol in a diesel task around Edinburgh costs more than another. Why?
The four scenarios above are four different tasks, so no single quote for this would be honest. The scenario itself does most of the work of moving the cost. The share matters next, meaning how much of your tank is petrol, and then the location of your car and whether reaching it is safe for a technician.
Ahead of any quote, not after, come three questions: your fuel that went in, the amount, and if it has run. That is why. Those replies are what change a range into one firm number.
About Edinburgh itself
Edinburgh is a coastal city in Scotland, situated on the southern shore of the Firth of Forth at an elevation of around 75 metres. Edinburgh sits in a strategic location, with nearby places such as Roxburghs Court, Greenside, and Old Town contributing to its urban landscape. Edinburgh is predominantly composed of flat housing, reflecting its dense and compact city centre. Edinburgh is a significant urban centre, with a population of approximately 198,614 people.
Edinburgh and City of Edinburgh: where our fuel drain cover runs
Roxburghs Court, Greenside and Old Town are among the spots around Edinburgh that the same vans work, answering petrol in diesel call-outs across Edinburgh's EH postcode area. No need to bring your car to us. Forecourts, supermarket car parks, lay-bys and your own drive are all spots where we work.
Edinburgh: still at the petrol pump?
Then, you couldn't be in a better place. Keep it off. Phone.