Soho: Petrol in a Diesel Car? How Worried to Be
Far less than you probably are, provided it has not been started. Everyone in Soho starts with "have I ruined it?", and the honest answer is generally no: petrol resting inside the tank of any diesel stays harmless till priming, cranking or driving draws it into the fuel system. To leave it like that, ring Petrol in Diesel and leave your motor switched off. Keep reading for three things: the effect petrol has inside a diesel motor, the signs of how far it has spread, and ways to make sure you never do it again.
Inside your engine: what petrol in a diesel does
On its way through a motor, diesel does two tasks. Lubricating comes before burning; it does both. What stops the surfaces inside your high-pressure pump and the injectors from grinding against each other is the diesel passing through them — they are designed to extremely fine clearances.
Petrol handles the first job poorly and the second not at all. Being less viscous than diesel, petrol strips out the protection a fuel system needs, so a pump running on the mixture wearing itself. It's equally made to resist igniting under compression — the reverse of what a diesel needs — which is where you get the knocking.
Together, those make the shape of the problem plain. Not contact but movement is what does the harm. All a tank with petrol in it amounts to is a fuel problem. A pump that has been labouring on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds moves on with your fuel to the fuel injectors downstream.
How serious is petrol in a diesel? Four situations our engineers see in Soho
Filled but never started — the best it gets. Just the tank has petrol in it, so the task is emptying your tank and flushing the fuel system where the vehicle sits. This situation can only really occur on a forecourt: anywhere else, your car got there by being driven.
Started for a moment, or just your ignition on. Your system has been primed, and so petrol has left the tank and reached the filter and the fuel lines. That's generally still a simple job — a drain, a flush, and your filter seen to.
Those few miles on the road were your pump running on fuel thinned by petrol the whole way. Tank, lines, filter, then clean fuel put through the whole circuit: that's the work, and the way the vehicle was driven counts as much as the miles. On the school run to Oasis Academy Wattville, the miles is small. Any mileage on the M5, under 3 miles from Soho, means the motor working hard throughout, and a run to Birmingham, under 3 miles away, is a very different job as well.
Knocking, a ragged idle, smoke, a throttle gone soft: driven until it complained. That is your engine telling you its fuel no longer is behaving like diesel. Leave it where it stops: a lay-by, a side street, the verge on Foundry Lane. What goes first is still the fuel drain and flush, and that deals with it, with permanent damage very uncommon when a car is stopped quickly.
Petrol in a diesel stories Soho motorists hear
Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. Topping up removes nothing; it gives you a bigger tank of the same mixture. A diesel fuel system doesn't tolerate petrol by percentage in the way that advice assumes.
Myth: "A modern diesel can cope with a bit of petrol." If anything, the opposite. Protection matters more on current diesels, not less, because their fuel passes through more precise components at higher pressure.
"It starts, it drives, so no harm done" — the myth that catches most motorists than any other. Feed diesel to a petrol engine and it generally will not run, so the motorist stops — and the harm stops with them. A diesel fed petrol generally starts, idles and drives away as if nothing has happened, while your pump grinds. Running does not mean fine.
Myth: "Add some two-stroke oil and drive the car home." It is an old workaround for a distinct issue. The petrol is still inside your tank afterwards, and what it has thinned is not put back.
The next start sends petrol back round your pump from your lines and the filter, where some of that sits after the motor has been run. That's why a DIY tank drain doesn't leave you sorted — a myth. And, a can of petrol drained at the roadside is genuinely risky.
Petrol in a diesel: how does it happen?
On purpose? Never. Through carelessness? Seldom, if ever. A diesel nozzle generally will not go into a petrol car, but the slimmer petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one error straightforward, and only in that direction.
When habit and the car stop matching, it happens. Courtesy car, hire car, or a vehicle that is new. One petrol and one diesel on the drive of the same household. A forecourt you know, but with its pumps laid out differently. A train to catch, and a hurried fill on the way to The Hawthorns. Years of petrol motors behind you, a diesel Volkswagen Golf in front of you at the forecourt for its first tank — that's when. With rain, a call arriving, or children to deal with, your hand just does what it always has.
Next time you fill up around Soho: preventing petrol in a diesel
- Green for unleaded and black for diesel is normal in the UK — but not on every forecourt. Trust the label on the pump, not the colour.
- The first fill in a strange car is the time to check the filler flap — inside it, or on the cap, plenty of cars state which fuel to use.
- Mark your key. In a house with one of each, a coloured fob or a sticker on your diesel's key does more than any amount of intending to remember.
- It seems daft and it does the trick: on your first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the petrol pump.
- Put your phone away. This is an easy mistake to make while you are thinking about something else.
- Add-on devices exist for motors without one, and some diesels come with a filler that won't accept a petrol nozzle. Helpful — but a backstop only, never a reason to stop checking the label.
- Stop the moment you realise. Less petrol inside your tank means a thinner blend. It doesn't change what to do next, which is still not to fire it up.
Petrol already in a diesel in Soho? Start here
Short and simple, then, is the order of things. Never start it, and don't turn your ignition on. Still at the forecourt, at JET or anywhere else? Ask the attendants to help you push the car away from the petrol pump. Next, 0333 366 0103. We will ask what went in, about how much, and if it has been run.
Say so if it was AdBlue rather than petrol: it is a separate fault, with its own page for Soho, since AdBlue brings corrosion and deposits instead of lost lubrication.
Soho petrol in a diesel tasks: why one costs more than another
Four separate tasks sit behind the four scenarios above — which is why there is no fair single price. What shifts the cost is chiefly which of them you're in. Two things come after that: the petrol that got in as a proportion of what the tank holds, then the place the car is in and whether a van can reach it safely.
Before any quote, not after, we ask three questions: the fuel that was put in, the amount, and whether it's run. That's why. Those replies are what change a range into one firm number.
About Soho itself
Soho is a suburban area in the West Midlands, situated near the River Rea and close to the city of Birmingham. Soho sits at an elevation of around 136 metres, with terraced housing being the predominant type of accommodation in the area. Soho is located near other local places such as Black Patch and Sandwell, and is approximately 2.5 miles from Birmingham city centre.
Across West Midlands and around Soho: fuel drain cover
Petrol in diesel jobs in Soho — part of the B postcode area — go to vans that likewise cover the spots around it, Black Patch, Merry Hill and Sandwell included. A forecourt, a supermarket car park, a lay-by or your own driveway are all spots our engineers work, and the vehicle doesn't need to move to us.
Soho: still at the petrol pump?
No position is better: that is where you now are. Phone, and keep it turned off.