--- title: Worried? Petrol in a Diesel Car St Boswells canonical: https://www.petrolinadieselcar.co.uk/petrol-in-diesel/st-boswells-scottish-borders/ location: St Boswells county: Scottish Borders latitude: 55.570960 longitude: -2.645610 service: Petrol in a Diesel Car updated: 2026-10-08 --- # Should You Worry? Petrol in a Diesel Car in St Boswells Far less than you likely are, if it has not been started. Petrol sitting in a diesel tank does nothing to the motor till something draws it through your fuel system — the ignition priming your pump, your starter, or driving itself. So the honest answer to the first query everyone in St Boswells asks, "have I ruined it?", is generally no. Leave the motor off and call Petrol in Diesel — that keeps it that way. The rest of this page explains what petrol actually does to a diesel, how to judge how far it has got, and how to make sure it doesn't happen to you a second time. ## Petrol in a diesel: what does it do to the motor? Passing through an engine, diesel is doing two things at the same time. It protects first, and after that does it burn. What keeps the surfaces inside the high-pressure fuel pump and your injectors from wearing down against one another is your diesel flowing through them — they're built to extremely fine tolerances. The second job petrol does not do at all, and the first it does poorly. The rattling comes from petrol being made not to ignite when compressed, which is exactly the reverse of what a diesel needs. On top of that it is runnier than diesel, it strips out the lubrication your system rests on, and any pump running on that mixture is wearing itself. Taken together, they show what shape the trouble has. It's circulation that causes the damage, not contact. All a tank with petrol in it amounts to is a fuel issue. The start of a mechanical problem is a pump that has been labouring on that petrol — and whatever a worn pump sheds moves on with your fuel to your injectors beyond it. ## St Boswells, petrol in a diesel: four situations, from mild to major Filled up, and never started: nothing beats it. At a forecourt, and genuinely only there, that petrol is still confined to the tank — since anywhere else your car was driven to get to it. The task is emptying and purging on the spot. Started for a moment, or only the ignition on. With your system primed, the lines and filter now hold petrol that has come from that tank. Still generally simple: drain, flush, and the fuel filter sorted. Those few miles driven were the pump running on fuel weakened by petrol the whole way. The work is that tank, your lines, the fuel filter and clean fuel through the entire system, and how hard your car was driven matters as much as how far. Driving the children to the local primary school is one kind of trip. Getting as far as Edinburgh, under 50 miles away, makes a very different task — as does any mileage on the M8, under 50 miles from St Boswells, with the motor working hard all the way. It complained, and only then stopped: smoke, rattling, a throttle gone soft, an idle gone lumpy. That's the motor telling you its fuel no longer is behaving like diesel. Stop wherever you are — the verge on Main Street, a lay-by, a side street — then leave the car there. Permanent damage is very unusual if a vehicle is stopped quickly, and the fuel drain and flush-through that still go first take care of it. ## What St Boswells motorists get told about petrol in a diesel — and the myths in it "Top it up the rest of the way with diesel and it will be fine" — a myth. It will not. Topping up takes out nothing; it gives you a fuller tank of the same mixture. That guidance presumes a diesel fuel system handles petrol by percentage. It does not. Myth: "A current diesel can cope with a bit of petrol." If anything, the reverse. Lubrication matters more on newer diesels, not less, because their fuel runs through smaller components at higher pressure. "It starts, it drives, and so no harm done" — the myth that trips up most motorists than any other. A petrol motor fed diesel usually will not run, and so the motorist stops and the damage stops with them. Feed petrol to a diesel and it normally starts, ticks over and pulls away like nothing happened — all the while its pump wears. Being able to run isn't the same as being fine. "A drop of two-stroke oil and drive it home" — a myth, taken from a fix from years ago, for a different problem. What petrol has thinned stays thinned, and the petrol remains in that tank anyway. Myth: "Drain that tank yourself and you're sorted." After the motor has been run, some of that petrol is no longer in the tank: it is in the filter and your lines, and it goes right back through your pump at the next start. It's also genuinely hazardous to drain petrol into a can at the roadside. ## Petrol in a diesel: how does it occur? No one does it on purpose, and it is rarely carelessness. A diesel nozzle mostly will not go into a petrol car, yet the narrower petrol nozzle goes into the filler of a diesel almost without resistance — so forecourts make this one error easy, and just in that direction. The moment habit stops matching the vehicle is the moment it occurs. A car that's new to you — hired, on loan as a courtesy car, or just bought. A household with one petrol and one diesel on the drive. The pumps in a different order on a well-known forecourt. A hurried fill en route to Tweedbank with a train to catch. The first fill-up in a diesel Volkswagen Passat after years of driving petrol is exactly the moment it takes place. With rain, a call coming in, or children to deal with, the hand just does what it has always done. ## Avoiding petrol in a diesel next time you fill up around St Boswells - Green for unleaded and black for diesel is normal in the UK — but not on each forecourt. Trust 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 cars print the fuel there. - One of each in the home? Mark your key to your diesel — a coloured fob, a sticker — since meaning to remember isn't enough. - It seems daft and it does the trick: on your first fill in a new or hired car, say "diesel" out loud before you lift the nozzle off the petrol pump. - Thinking about something else is when this becomes an easy mistake to make, and so tuck the phone away and keep your mind on the pump. - Some diesels come with a filler designed to reject a petrol nozzle, and devices you can add exist for cars without one. Such an inhibitor helps up to a point — as a safety net, not a reason to stop reading the petrol pump. - Noticing it mid-fill? Stop at once. A thinner blend results from less petrol inside your tank, yet the next step stays the same: do not start the vehicle. ## Petrol already in a diesel in St Boswells? Start here Short and simple, then, is the order of things. Do not switch the ignition on, and do not crank it. The attendants on the forecourt — whether at the nearest petrol station itself or wherever you filled up — will normally help roll it away from the pump if you ask. Then phone 0333 366 0103 and tell us what went in, about how much, and if it has run. If it was AdBlue instead of petrol, say so. That is a separate problem — corrosion and deposits rather than lost protection — and it has its own page for St Boswells. ## One petrol in a diesel job around St Boswells costs more than another. Why? A fair single price does not exist here: four scenarios, four separate tasks. What moves your cost is mostly which of them you are in. Where the vehicle is matters too, and whether a technician can safely reach it, after the share of petrol to what that tank holds. That's why our technicians ask three queries before costing rather than after: what was put in, how much, and if it has run. Those answers turn a range into a straight figure. ## About St Boswells, briefly St Boswells is a village in the Scottish Borders, situated on the banks of the River Tweed at an elevation of around 90 metres. St Boswells has a mix of housing types, with semi-detached homes being particularly prevalent, and is located near the towns of Dryburgh and Newtown St Boswells. St Boswells is close to the A68 road and has a population of approximately 1278 residents. St Boswells is also within commuting distance of Edinburgh, which is around 33.8 miles away. ## Across Scottish Borders and around St Boswells: fuel drain cover Petrol in diesel call-outs around St Boswells — part of the TD postcode area — go to vans that also cover the spots around it, Dryburgh, Newtown St Boswells and Charlesfield among them. A forecourt, a supermarket car park, a lay-by or your own drive are all locations our technicians work, and the car does not need to come to us. ## At the petrol pump around St Boswells, still? The best position there is, then — that's where you are. Keep it off. Ring.