How Worried Should You Be? Petrol in a Diesel Car in St Gwynans
Far less than you likely are, if it hasn't been started. "Have I ruined it?" is the first thing anyone in St Gwynans asks, and the honest answer is generally no, because petrol left in a diesel tank hurts nothing till it's dragged through the system — by ignition priming, by your starter, or by driving. Petrol in Diesel is who to call, with your engine kept off, so it remains that way. What petrol actually does to a diesel, how to gauge how far it has travelled, and how to keep it from happening again: that's the remainder of this page.
Inside the engine: what petrol in a diesel does
Diesel does two tasks on its way through an engine. It ignites, and before it combusts it lubricates. Very fine tolerances go into your injectors and your high-pressure pump, and only your diesel flowing through stops those surfaces grinding together.
The second task petrol doesn't do at all, and the first it does badly. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, leaving a pump on that mixture to wear itself. It is also made to resist igniting under compression — the reverse of what a diesel needs — which is why you hear the clattering.
The shape of the trouble is clear once you put those together. Not contact but circulation is what does the harm. Any tank with petrol in it is a fuel problem. After the pump has been working on that petrol, a mechanical problem has started: anything shed by a pump that is wearing is carried downstream to the fuel injectors with the fuel.
Petrol in a diesel around St Gwynans: how bad is it? Four cases
Filled but never started — the best it gets. Being at a forecourt is what makes this the case: elsewhere, the vehicle has been driven there to begin with. With that petrol kept inside that tank alone, it is cleared and cleaned right where it stands, and nothing more is needed.
The ignition turned on, or a short start. With the system primed, your lines and filter already hold petrol that came from your tank. Usually nothing more than emptying, flushing and sorting the fuel filter, and so still easy.
A couple of miles driven, and your pump has spent each of them working on diluted fuel. Tank, lines, filter, then fresh fuel run through the entire system: that's this work, and the way the car was driven counts as much as the mileage. Short trips, like the school run to the local primary school, are one thing. Driving as far as Bangor, under 15 miles away, makes a very different job — as does any mileage on the Moreton Spur, under 50 miles from St Gwynans, with your engine running hard the whole time.
Driven until it complained. Clattering, an uneven idle, smoke, a throttle that has gone soft. The fuel isn't acting like diesel any more, and your motor is saying so. Leave it where it stops: a lay-by, a side street, the verge on Ysguborwen Road. Lasting damage is very uncommon if a car is pulled over quickly, and the drain and flush that still go first deal with it.
What St Gwynans people get told about petrol in a diesel — and the stories in it
"Top it up the rest of the way with diesel and it'll be fine" — a myth. It won't. Nothing is removed by topping up — you are left with a fuller tank, still the same mix. A diesel fuel system doesn't tolerate petrol by percentage in the way that advice presumes.
Myth: a current diesel copes with a bit of petrol. Rather, the opposite. Lubrication matters more on newer diesels, not less, since their fuel runs through more precise components at higher pressure.
The myth that catches motorists off guard: if it starts and drives, it must be unharmed. Feed diesel to a petrol engine and it usually will not run, and so the driver stops — and the harm stops with them. A diesel fed petrol usually starts, ticks over and drives away as though nothing has happened, while the pump grinds. A running engine doesn't mean fine.
"A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a different problem. None of what petrol diluted gets put back by it — and afterwards, that tank still contains the petrol.
"Drain it yourself and you are sorted" — a myth, because after it has been running some petrol lies in the fuel filter and lines, ready to go right back through your pump on your next start. Also, a can of petrol drained by the roadside is genuinely risky.
Why petrol in a diesel occurs at all
It's rarely carelessness, and nobody does it on purpose. The forecourt makes it simple: the petrol nozzle is the slimmer of the two, and it slides into a diesel filler with almost no resistance, while a diesel nozzle mostly will not go into a petrol motor at all. So the error runs one way.
Routine and the car falling out of step is when it takes place. Courtesy car, hire car, or a vehicle that's new. A household with one petrol and one diesel on the drive. Your usual forecourt, its pumps now in a different order. A train to catch, and a rushed fill on the way to Penmaenmawr. A new-to-you diesel Renault Clio, its first fuelling, and a motorist used to petrol: exactly when it happens. Add a back seat full of kids, a phone call or rain, and the hand wins.
St Gwynans drivers: how to avoid petrol in a diesel next time
- Not every forecourt in the UK keeps to green for unleaded and black for diesel, though most generally do. Check the petrol pump's label; the colour is just a hint.
- Many motors state the fuel type inside the filler flap or on the cap, and so check it on the first fill in any motor you don't know.
- One of each in the house? Label your key to your diesel — a coloured fob, a sticker — because meaning to remember isn't enough.
- Say it before you lift it. On your first fill in a new or hired car, say "diesel" out loud before you take the nozzle off the petrol pump. It sounds daft and it works.
- Tuck your 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 have a filler built to block a petrol nozzle, and add-on devices exist for cars without one. They are a safety net, not a reason to stop reading the pump.
- Noticing it halfway? Stop at once. A weaker mixture follows from less petrol inside that tank, but your next step stays the same: don't crank it.
Already put petrol in a diesel around St Gwynans?
Then the order of things is short. Do not turn your ignition on, and do not crank it. Ask the attendants to help you roll it clear of the petrol pump if you are still on the forecourt, whether that's Shell or anywhere else. Next, 0333 366 0103. We will ask what got in, roughly how much, and if it's been run.
If it was AdBlue instead of petrol, say so. That's a separate problem — corrosion and deposits rather than lost lubrication — and it has its own page for St Gwynans.
St Gwynans petrol in a diesel jobs: why one costs more than another
The four situations above are four separate jobs, so no single price for this would be fair. Chiefly, the cost moves with which one you're in. Next it is the ratio — how much petrol was put in against how much the tank takes — and then where your car is and whether our van can reach it safely.
What went in, how much, and whether it has run — three questions our engineers ask before costing, not after, for precisely that reason. The answers change a range into a straight figure.
About St Gwynans, for a moment
St Gwynans is a coastal suburban area in Conwy, Wales, situated near the towns of Dwygyfylchi and Penmaenmawr. St Gwynans has a population of around 1403 people and is characterised by semi-detached housing. St Gwynans is located close to Bangor, the nearest city, and is approximately 200 miles from London. St Gwynans sits at a low elevation of 28 metres above sea level, reflecting its coastal setting.
Across Conwy and around St Gwynans: fuel drain cover
Dwygyfylchi, Capelulo and Penmaenmawr are among the spots around St Gwynans that the same vans work, answering petrol in diesel jobs across St Gwynans's LL postcode area. A forecourt, a supermarket car park, a lay-by or your own driveway are all locations our technicians drain, and the vehicle does not need to move to us.
Still at the petrol pump around St Gwynans?
The best spot there is, then — that's where you are. Keep the vehicle switched off, and ring.