How Worried Should You Be? Petrol in a Diesel Car in Hyde Park Corner
Far less than you likely are, if it has not been started. "Have I wrecked it?" is the first question everyone in Hyde Park Corner asks, and the truthful answer is generally no, since petrol resting in a diesel tank harms nothing till it is dragged through the fuel system — by ignition priming, by your starter, or by being driven. Petrol in Diesel is who to phone, with the engine kept off, and so it stays that way. Keep reading for three things: the effect petrol has inside a diesel engine, the signs of how far it has got, and the way to make sure you never repeat it.
Petrol in a diesel: what does it do to the engine?
On its way through a motor, diesel has two tasks. It lubricates to begin with, and only then does it burn. Very fine gaps go into your injectors and your high-pressure pump, and just your diesel running through stops their surfaces grinding together.
Poorly at the first, not at all at the second: that's petrol. The knocking comes from petrol being designed not to ignite when compressed, which is exactly the opposite of what a diesel needs. On top of that it is thinner than diesel, it strips out the protection the fuel system depends on, and any pump working on that mixture is wearing itself.
Seen together, they show the shape the trouble takes. Contact doesn't do the harm — circulation does. Any tank with petrol in it is a fuel problem. Whatever a worn pump sheds travels on, borne by the fuel, into your injectors downstream, which is why a pump that has been working on the petrol is where a mechanical problem starts.
How serious is petrol in a diesel? Four scenarios our technicians see around Hyde Park Corner
Fuelled, and never started: no case is better. Only your tank has petrol in it, and so the task is emptying your tank and cleaning the fuel system where the vehicle sits. This scenario can only truly happen at a forecourt: anywhere else, the vehicle got there by being driven.
Your ignition turned on, or a brief start. With your system primed, the fuel lines and filter now contain petrol that has come from the tank. That is generally still a simple task — a drain, a flush, and your filter seen to.
Those few miles on the road meant your pump running on fuel weakened by petrol throughout. Tank, lines, filter, then fresh fuel run through the whole system: that's this work, and the way the car was driven counts as much as the mileage. Driving the kids to St George's Hanover Square CofE Primary School is one kind of trip. A run as far as Westminster, under 3 miles away, is a very different task. So is any distance on the M4, under 10 miles from Hyde Park Corner, where the engine has been working hard the whole time.
Driven till it complained. Knocking, an uneven idle, smoke, a throttle that has gone soft. That's the engine telling you its fuel no longer is acting like diesel. Pull up wherever you are — the verge on Grosvenor Crescent, a lay-by, a side street — then leave it where it is. Long-term damage is very rare when a car is pulled over quickly, and the drain and flush-through that still go first deal with it.
Stories Hyde Park Corner motorists hear about petrol in a diesel
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It won't. Nothing comes out when you top up — the tank just carries more of the same blend. The assumption behind the advice — that diesel fuel systems tolerate petrol by percentage — is wrong.
Myth: "A newer diesel can cope with a bit of petrol." If anything, the reverse. Finer parts and higher pressure are the way a newer diesel runs its fuel, and that makes the protection matter more, not less.
This is the one that catches drivers. Myth: "If it starts and drives, there's no harm done." Diesel in a petrol motor generally leaves a motor that will not run: the driver stops, and so does the damage. While the pump grinds, a diesel fed petrol normally starts, ticks over and drives away as though nothing has happened. Being able to run isn't proof of being fine.
An outdated fix for a separate issue lies behind this one. Myth: "Add some two-stroke oil and drive it home." That petrol is still inside the tank afterwards, and whatever it has thinned isn't put back.
Once your engine has run, part of the petrol sits in the filter and the fuel lines, not your tank — and your next start sends it right back through the pump. So the myth "drain the tank yourself and you're sorted" doesn't stand up. It's also truly risky to drain petrol into a can at the roadside.
How does petrol in a diesel happen?
Nobody does it on purpose, and it is seldom carelessness. A diesel nozzle generally will not fit a petrol motor, but the narrower petrol nozzle goes into the filler of a diesel nearly without resistance — so forecourts make this one error straightforward, and just in one direction.
The moment routine stops matching your car is the moment it happens. A vehicle that is new to you — hired, on loan as a courtesy car, or just bought. One petrol and one diesel on the driveway of the same household. The pumps in a different order on a well-known forecourt. A train to catch, and a hurried fill en route to London Victoria. The first fill-up in a diesel Volkswagen Passat after years of driving petrol is exactly the moment it takes place. The hand does what it has always done when you add rain, a phone call or a back seat full of kids.
Preventing petrol in a diesel next time you fill up in Hyde Park Corner
- Not every forecourt in the UK follows green for unleaded and black for diesel, though most generally do. Read the pump's label; the colour is only a hint.
- In a vehicle you don't know, look inside the flap over the filler or at the cap before your first fill: many cars print the fuel there.
- One of each in the household? Label the key to your diesel — a coloured fob, a sticker — since meaning to remember is not enough.
- Before the nozzle leaves the petrol pump the first time you fuel a hired or new motor, say "diesel" aloud. Daft, yes, but it works.
- Put the phone away. This is an easy mistake to make while you're thinking about something else.
- A misfuel inhibitor helps, up to a point. Some diesels come with a filler built to refuse a petrol nozzle, and add-on devices are available for motors without one. They are a backstop, not a reason to stop reading the petrol pump.
- Spotting it mid-fill? Stop there and then. A thinner mix results from less petrol inside your tank, but your next stage remains the same: don't start the car.
Put petrol in a diesel around Hyde Park Corner already?
Then the order of things is brief. Starting it is out, and so is turning on the ignition. Still on the forecourt, at Esso or anywhere else? Ask the attendants to help you push the vehicle away from the petrol pump. Then call 0333 366 0103 and tell us what got in, roughly how much, and if it has run.
If it was AdBlue rather than petrol, say so. That is a separate fault — corrosion and deposits and not lost protection — and it has its own page for Hyde Park Corner.
Hyde Park Corner petrol in a diesel tasks: why one costs more than another
The four situations above are four separate tasks, so no single price for this would be fair. What shifts the cost is mostly 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 spot the vehicle is in and whether a van can reach it safely.
What was put in, how much, and if it has run — three queries our engineers ask before quoting, not after, for precisely that reason. Given those answers, there is a straight figure rather than a range.
About Hyde Park Corner
Hyde Park Corner is a suburban area in central London, situated on the southern edge of Hyde Park and overlooking the Serpentine Lake. Hyde Park Corner sits at a relatively low elevation of around 20 metres, close to the heart of the city. Hyde Park Corner is surrounded by other affluent neighbourhoods, including Belgravia, Mayfair, and St James's, and is home to a population of approximately 3610 people, predominantly residing in flats.
Fuel drain cover in Hyde Park Corner and across Greater London
Hyde Park Corner waits in the SW1X postcode area, and the vans that answer petrol in diesel call-outs there work the locations around it as well — Belgravia, Mayfair and St Jamess among them. The vehicle does not need to come to us: we drain at a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
At the pump in Hyde Park Corner, still?
Then, you could not be in a better position. Keep the vehicle switched off, then ring.