--- title: Old Woking: Petrol in a Diesel Car, Explained canonical: https://www.petrolinadieselcar.co.uk/petrol-in-diesel/old-woking-surrey/ location: Old Woking county: Surrey latitude: 51.302240 longitude: -0.539510 service: Petrol in a Diesel Car updated: 2026-10-11 --- # How Worried Should You Be? Petrol in a Diesel Car in Old Woking Far less than you probably are, if it hasn't been started. Everyone around Old Woking begins with "have I ruined it?", and the honest answer is usually no: petrol resting inside that tank of a diesel remains harmless until priming, cranking or driving pulls it into the system. To leave it that way, call Petrol in Diesel and leave the engine switched off. What petrol actually does to a diesel, how to judge how far it's gone, and how to stop it from happening again: that's the rest of this page. ## Petrol in a diesel: what does it do to the motor? On its way through an engine, diesel has two jobs. It burns, and before it combusts it lubricates. Designed to extremely fine clearances, the fuel injectors and the pump depend on your diesel flowing through them to keep their surfaces from wearing against one another. The second job 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 running on the mixture to wear itself. It is also made to resist igniting under compression — the reverse of what a diesel needs — which is where you hear the knocking. The shape of the issue is plain when you put those together. It's movement that causes the damage, not contact. Where the petrol is only inside your tank, it's a problem of fuel, nothing more. A pump that has been running on that petrol is the start of a mechanical one, and whatever a worn pump sheds travels on with the fuel to your injectors further on. ## Petrol in a diesel in Old Woking: how bad is it? Four situations Filled up, not once started. The best case there can be. Being on a forecourt is what makes this possible: elsewhere, the vehicle has been driven there to begin with. With that petrol held inside the tank alone, it is emptied and cleaned right where it stands, and nothing more is needed. Your ignition turned on, or a brief start. Once primed, the system has pulled petrol from the tank as far as your filter and the fuel lines. That is normally still an easy job — a drain, a flush, and your filter seen to. Those few miles on the road were the pump running on fuel thinned by petrol throughout. The work is that tank, your lines, the filter and fresh fuel through the entire system, and how hard the car was driven counts as much as how far. A school run to Kingfield Primary School is one thing. Very different once more: a run to Westminster, under 25 miles away, or some miles on the M25, under 5 miles from Old Woking, where the engine never stopped running hard. It complained, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone lumpy. The fuel isn't behaving like diesel any more, and your motor is telling you. Pull up on the spot — on the verge on St Peters Road, at the kerb, down a side road — and don't move it. Long-term damage is very uncommon when a car is stopped early, and the fuel drain and flush-through that still come first sort it out. ## Stories Old Woking motorists hear about petrol in a diesel Myth: topping up to full with diesel makes it fine. It does not. Nothing comes out when you top up — that tank just carries more of the same mixture. Percentage isn't how a diesel fuel system copes with petrol, however much that advice assumes. Myth: "A newer diesel can cope with a bit of petrol." If anything, the opposite. Protection matters more on newer diesels, not less, because their fuel runs through finer components at higher pressure. This is the one that catches motorists. Myth: "If it starts and drives, there is no damage done." Feed diesel to a petrol engine and it normally will not run, so the driver stops — and the damage stops with them. A diesel fed petrol generally starts, ticks over and drives away as if nothing has happened, while the pump wears. A running engine doesn't mean fine. An outdated fix for a different fault lies behind this one. Myth: "Add some two-stroke oil and drive the vehicle home." The petrol is still inside the tank afterwards, and whatever it has weakened is not put back. "Drain it yourself and you're sorted" — a myth, since after it's been running some petrol lies in your filter and lines, waiting to go straight back through the pump on the next start. It is also really dangerous to drain petrol into a can by the kerbside. ## How petrol ends up: petrol in a diesel On purpose? Never. Through carelessness? Seldom, if ever. A diesel nozzle mostly will not fit a petrol motor, yet the slimmer petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one error straightforward, and only in that direction. It takes place when routine and the vehicle stop matching. Any vehicle that's new to you — hired, on loan as a courtesy car, or brand new. Two cars on one drive, one petrol, one diesel. The pumps in a different order on a well-known forecourt. Fuelling up in a hurry en route to Woking, with a train to catch. Years of petrol motors behind you, a diesel Volkswagen Golf in front of you at the forecourt for its first tank — that is when. With rain, a call coming in, or children to deal with, the hand just does what it has always done. ## Old Woking motorists: how to avoid petrol in a diesel next time - Green for unleaded and black for diesel is normal in the UK — yet not on every forecourt. Go by the label on the petrol pump, not the colour. - Many vehicles state the fuel type inside the filler flap or on the cap, so check it on the first fill in any car you do not know. - Good intentions do less than a sticker or a fob in a bright colour on the diesel's key if a house has one of each. So label it. - "Diesel", aloud, before you lift the nozzle — every time a new or hired car needs its first tank. It sounds silly. It works. - Put your phone away. This is an easy mistake to make whilst you're thinking about something else. - Add-on devices exist for vehicles without one, and some diesels come with a filler that won't take a petrol nozzle. Useful — but a backstop only, never a reason to stop checking the label. - As soon as you realise, stop: less petrol in that tank means a thinner blend. What to do next doesn't change, though — still do not fire it up. ## Already put petrol in a diesel around Old Woking? Then the order of things is brief. Leave it unstarted, with your ignition switched off too. Ask the attendants to help you push it clear of the pump if you're still on the forecourt, whether that's Shell or somewhere else. What went in, roughly how much, and whether it has run: tell us those when you call 0333 366 0103. Corrosion and deposits form the issue with AdBlue, where petrol brings lost lubrication. So if it was AdBlue, say so — and see its own Old Woking page. ## One petrol in a diesel job around Old Woking costs more than another. Why? There's no honest single price for this, because the four scenarios above are four separate tasks. What shifts your cost is mostly which of them you're in. Next it is the share — how much petrol got in against how much the tank takes — and after that where the car is and whether our van can get to it safely. What was put in, how much, and if it has run — three queries our technicians ask before costing, not after, for precisely that reason. A range turns into a straight figure when those replies are in. ## About Old Woking itself Old Woking is a suburban area in Surrey, situated on the riverside at an elevation of 28 metres, with semi-detached housing being the predominant type of accommodation. Old Woking lies approximately 22.7 miles from London and is close to nearby places such as Cartbridge and Kingfield. Old Woking has a population of around 3742 residents and is part of the wider urban area surrounding Westminster. Old Woking's location near the river has influenced its development over time. ## Fuel drain cover in Old Woking and across Surrey Old Woking rests in the GU postcode area, and our vans that answer petrol in diesel call-outs there work the locations near it as well — Cartbridge, Kingfield and Hockering Estate among them. You need not move the car to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all spots we drain. ## Still at the pump in Old Woking? No position is better: that's where you are. Ring, and keep it switched off.