How Worried Should You Be? Petrol in a Diesel Car in Mount Hawke
Not started? Then less worried than you probably feel. Everyone around Mount Hawke starts with "have I ruined it?", and the fair answer is normally no: petrol left inside the tank of a diesel remains harmless until priming, cranking or driving draws it into your fuel system. Leave the motor off then ring Petrol in Diesel — that keeps it like that. Below, this page sets out what petrol actually does inside a diesel, how far it might have got, and how to stop it happening to you again.
What petrol in a diesel does to your engine
Passing through an engine, diesel is doing two things at once. Before it combusts, it protects — and then it combusts. Extremely fine gaps go into your injectors and the high-pressure pump, and only the diesel running through stops those surfaces grinding together.
The second task petrol does not do at all, and the first it does poorly. Being less viscous than diesel, petrol strips away the protection a fuel system needs, so a pump on that mixture wearing itself. It's equally made to resist igniting under compression — the opposite of what a diesel needs — which is where you get the clattering.
Combined, those make the shape of the issue clear. The damage is done by movement, not by contact. Where that petrol is only inside the tank, it's a problem of fuel, nothing more. Once your pump has been working on that petrol, a mechanical fault has started: anything shed by a pump that is wearing travels onward to the injectors with the fuel.
Mount Hawke, petrol in a diesel: four cases, from mild to serious
Fuelled but not once started — the best it gets. Only the tank has petrol in it, so the job is emptying your tank and cleaning your system where the vehicle sits. This situation can only really take place on a forecourt: anywhere else, the vehicle got there by being driven.
Your ignition switched on, or a short start. Once primed, the fuel system has drawn petrol from your tank as far as the fuel filter and your lines. Drain, flush, deal with the filter: still usually simple.
Those few miles on the road were the pump working on fuel weakened by petrol the whole way. The work is your tank, the lines, the filter and clean fuel through the entire circuit, and how hard the vehicle was driven matters as much as how far. Short trips, like the school run to Mount Hawke Academy, are one thing. Any miles on the M5, over 50 miles from Mount Hawke, means the engine working hard throughout, and a run to Truro, under 10 miles away, is a very different job too.
Driven on until it complained — clattering, smoke, an uneven idle, a soft throttle. The fuel isn't acting like diesel any more, and your motor is telling you. Pull up on the spot — on the verge on Fore Street, at the kerb, down a side road — and don't move it again. The fuel drain and flush still go first, and they sort it out: when a car is pulled over early, lasting damage is very rare.
Mount Hawke people and that petrol in a diesel myths they hear
Myth: topping up to full with diesel makes it fine. It doesn't. A fuller tank of the same mixture is all it gives, because topping up removes nothing. That advice presumes a diesel fuel system tolerates petrol by percentage. It does not.
Myth: "A newer diesel can cope with a bit of petrol." If anything, the opposite. Smaller components and higher pressure are the way a newer diesel runs its fuel, and that makes the lubrication matter more, not less.
This is the one that catches drivers. Myth: "If it starts and drives, there is no harm done." A petrol engine fed diesel generally will not run, so the driver stops and the harm stops with them. Feed petrol to a diesel and it generally starts, idles and drives away like nothing happened — all while its pump wears. Running is not the same as fine.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a different issue. It doesn't put back what petrol has weakened, and the petrol is still in the tank after that.
"Drain it yourself and you're sorted" — a myth, because after it has been running some petrol sits in the fuel filter and lines, ready to go right back through your pump at your next start. Also, a can of petrol filled by the roadside is genuinely dangerous.
How it happens: petrol in a diesel
A careless moment is rarely the cause, and no one means to do it. A diesel nozzle mostly won't fit a petrol motor, 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 one direction.
When routine and your car stop matching, it occurs. Hire cars, courtesy cars, and vehicles that are new to you. Two vehicles on one drive, one petrol, one diesel. Your usual forecourt, its pumps now in a different order. A train to catch, and a hurried fill on the way to Redruth. The first fill-up in a diesel Renault Clio after years of driving petrol is precisely the moment it occurs. Your hand repeats what it has always done once you add rain, a phone call or a back seat full of kids.
Next time you fill up around Mount Hawke: preventing petrol in a diesel
- Not every forecourt in the UK follows green for unleaded and black for diesel, though most generally do. Check the pump's label; the colour is just a clue.
- In a car you do not know, look inside the flap over your filler or at the cap before the first fill: plenty of motors state the fuel there.
- Good intentions count for less than a sticker or a fob in a vivid colour on your diesel's key when a household has one of each. So mark it.
- It sounds silly and it works: on the first fill in a new or hired car, say "diesel" aloud before you take the nozzle off the pump.
- Put the phone away. This is an easy mistake to make while you're thinking about something else.
- Add-on devices exist for cars without one, and some diesels come with a filler that will not take a petrol nozzle. Useful — but a safety net at best, never a reason to stop checking the label.
- Less petrol makes a weaker blend, and so stop the moment you notice — though remembering that the next step is unchanged. It is still not to fire it up.
Mount Hawke: already put petrol in a diesel?
Short and simple, then, is the order of things. Leave it unstarted, with the ignition switched off as well. If you are still at the forecourt — Esso or anywhere else — ask the staff to help you roll it away from the pump. What went in, about how much, and if it's run: tell us that when you call 0333 366 0103.
If it was AdBlue and not petrol, say so. That's a different problem — corrosion and deposits and not lost protection — and it has its own page for Mount Hawke.
Mount Hawke petrol in a diesel tasks: why one costs more than another
An honest single price does not exist here: four situations, four separate tasks. Chiefly, the cost moves with which one you are in. Next it's the proportion — how much petrol was put in against how much the tank holds — and then where the vehicle is and whether our van can reach it safely.
Before any quote, not after, we ask three questions: the fuel that was put in, the volume, and whether it has run. That's why. Those replies turn a range into a straight figure.
About Mount Hawke
Mount Hawke is a small village in Cornwall, situated on the coastal fringe of the South West region, with Banns Vale and Mingoose nearby. Mount Hawke sits at an elevation of around 90 metres, overlooking the surrounding countryside and close to the larger town of Truro. Mount Hawke has a mix of housing types, but terraced homes are particularly prevalent in the village. Mount Hawke is located approximately 7 miles from Truro and 237 miles from London.
Across Cornwall and in Mount Hawke: fuel drain cover
Mount Hawke waits in the TR postcode area, and our vans that answer petrol in diesel jobs there work the spots near it as well — Banns Vale, Mingoose and Menagissey among them. The car doesn't need to come to us: our technicians drain on a forecourt, in a supermarket car park, in a lay-by or on your own drive.
Still at the pump in Mount Hawke?
Nothing beats it: that is where you are. Keep it off. Ring.