How Worried Should You Be? Petrol in a Diesel Car in Whiteflat
Probably less than you already are — provided nobody has started the vehicle. Till the ignition primes your pump, the starter cranks, or your car is driven, petrol in a diesel tank just rests there and does no harm. Which means the truthful reply to the first Whiteflat question — "have I ruined it?" — normally no. Leave your motor off then ring Petrol in Diesel — that keeps it like that. Below, you will find what petrol really does inside a diesel, how far it might have got, and how to stop it happening to you a second time.
The motor and petrol in a diesel: what happens
On its way through an engine, diesel has two tasks. Before it combusts, it protects — then it burns. Extremely fine clearances go into the injectors and the high-pressure fuel pump, and only your diesel running through stops their surfaces grinding together.
Petrol handles the first task badly and the second not at all. Being less viscous than diesel, petrol strips away the protection a fuel system needs, leaving a pump running on that mixture to wear itself. It is equally made to resist igniting under compression — the opposite of what a diesel needs — which is why you get the knocking.
Together, those make the shape of the trouble clear. The harm is done by movement, not by contact. A tank with petrol in it is a fuel issue. A pump that has been running on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds travels on with your fuel to your injectors downstream.
Four situations our engineers see around Whiteflat: how serious is petrol in a diesel?
The best case there is: filled up, never started. At a forecourt, and genuinely only there, that petrol is still limited to the tank — since everywhere else your car was driven to reach it. The task is emptying and purging on the spot.
Ignition on, or started for a moment. With the system primed, the lines and filter already hold petrol that came from the tank. Still usually simple: drain, flush, and the fuel filter sorted.
A few miles driven, and the pump has spent each of them labouring on thinned fuel. Distance is only half of that; how hard it was driven counts just as much. Either way this work runs to your tank, your lines, your filter and fresh fuel through the whole system. Driving the kids to the local primary school is one kind of trip. A run as far as Glasgow, under 50 miles away, is a very different job. So is any mileage on the M77, under 15 miles from Whiteflat, where the engine has been working hard the whole time.
It protested, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone ragged. What you are hearing is the motor reporting fuel that no longer behaves like diesel. Leave it wherever it stops: a lay-by, a quiet street, the verge on Newton Street. The fuel drain and flush-through still come first, and they sort it out: if a vehicle is pulled over early, lasting damage is very uncommon.
What Whiteflat drivers get told about petrol in a diesel — and the myths in it
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Nothing comes out when you top up — the tank simply holds more of the same blend. Percentage is not how a diesel fuel system tolerates petrol, whatever that guidance assumes.
"Modern diesels can handle a little petrol" — a myth, and closer to the opposite. Lubrication counts more on modern diesels, not less, because their fuel passes through more precise components at higher pressure.
The myth that catches drivers off guard: if it starts and drives, it must be unharmed. Diesel in a petrol motor normally leaves a motor that won't run: the driver stops, and so does the harm. A diesel fed petrol normally starts, idles and drives away as though nothing has happened, whilst your pump grinds. Fine and running aren't the same at all.
Myth: "Add some two-stroke oil and drive the vehicle home." It's an old fix for a separate problem. None of what petrol diluted gets put back by it — and later, your tank still contains the petrol.
Myth: "Drain that tank yourself and you're sorted." After your engine has been run, some of that petrol is no longer in that tank: it is in the fuel filter and your lines, and it goes right back through your pump on the next start. And, a can of petrol filled by the kerbside is truly hazardous.
How petrol ends up: petrol in a diesel
It is seldom carelessness, and nobody does it on purpose. A diesel nozzle mostly will not fit a petrol vehicle, but the smaller petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one error easy, and only in one direction.
Habit and your car falling out of step is when it happens. A new motor, a hire car or a courtesy car. A household with one petrol and one diesel on the drive. Your normal forecourt, its pumps suddenly in a different order. A train to catch, and a rushed fill on the way to Auchinleck. The first fill-up in a diesel Renault Megane after years of driving petrol is precisely the moment it takes place. Your hand does what it has always done when you add rain, a phone call or a back seat full of children.
Next time you fill up in Whiteflat: avoiding petrol in a diesel
- Green for unleaded and black for diesel is usual in the UK — but not on each forecourt. Go by the label on the petrol pump, not the colour.
- In a motor you don't know, look inside the flap over the filler or at the cap before your first fill: plenty of vehicles state the fuel there.
- Label your 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.
- "Diesel", aloud, before you lift the nozzle — each time a new or hired car needs its first tank. It sounds silly. It works.
- Mistakes like this are simple to make while your mind is on something else, and so your phone goes away.
- Up to a point, a misfuel inhibitor helps: some diesels come with a filler designed to reject a petrol nozzle, and add-on devices exist for the remainder. Treat it as a backstop, then keep checking the pump.
- As soon as you notice, stop: less petrol in that tank means a thinner mixture. What to do next doesn't change, though — still don't start the vehicle.
Put petrol in a diesel around Whiteflat already?
Short and simple, then, is the order of things. Do not turn the ignition on, and do not fire it up. Yet at the forecourt, at Thames or anywhere else? Ask the attendants to help you roll the vehicle clear of the petrol pump. Next, 0333 366 0103. We will ask what went in, about how much, and if it's been run.
Say so if it was AdBlue rather than petrol: it's a separate fault, with its own page for Whiteflat, since AdBlue brings corrosion and deposits instead of lost lubrication.
Why one petrol in a diesel task around Whiteflat costs more than another
The four situations above are four different jobs, so no single price for this would be honest. Which of them you are in is mostly what shifts your cost. Where the car is matters too, and whether a technician can safely get to it, after the share of petrol to what your tank holds.
That is why we ask three questions before pricing rather than after: what was put in, how much, and if it has run. Those replies are what turn a range into one firm number.
About Whiteflat and its setting
Whiteflat is a riverside locality in East Ayrshire, situated near the River Ayr at an elevation of around 120 metres. Whiteflat lies approximately 25 miles from Glasgow and is close to nearby places such as Catrine, Haugh, and Sorn. Whiteflat has a population of around 747 people and is characterised by predominantly terraced housing.
Across East Ayrshire and around Whiteflat: fuel drain cover
Whiteflat sits in the KA postcode area, and the teams that answer petrol in diesel call-outs there work the spots around it as well — Catrine, Haugh and Sorn among them. The vehicle does not need to move to us: we drain on a forecourt, in a supermarket car park, in a lay-by or on your own driveway.
In Whiteflat and still at the petrol pump?
The best position there is, then — that is where you are. Keep it off. Phone.