--- title: Uphill: Petrol in a Diesel Car, Explained canonical: https://www.petrolinadieselcar.co.uk/petrol-in-diesel/uphill-somerset/ location: Uphill county: Somerset latitude: 51.323130 longitude: -2.980710 service: Petrol in a Diesel Car updated: 2026-10-06 --- # Uphill: Petrol in a Diesel Car? How Worried to Be If it has not been started, worry far less than you likely are. Till your ignition primes your pump, your starter cranks, or the vehicle is driven, petrol in a diesel tank just waits there and does no harm. Which means the truthful reply to that first Uphill question — "have I ruined it?" — usually no. Petrol in Diesel is who to ring, with your engine left off, and so it stays that way. What petrol really does to a diesel, how to judge how far it's gone, and how to stop it from happening a second time: that's the rest of this page. ## Petrol in a diesel: what does it do to the engine? On its way through an engine, diesel has two tasks. It protects first, and after that does it burn. Designed to extremely fine clearances, the fuel injectors and the pump rely on the diesel moving through them to keep their surfaces from wearing against one another. Of those two jobs, petrol manages the first poorly and the second never. A pump working on a petrol mix is wearing itself out, because petrol is thinner than diesel and strips out the lubrication your fuel system depends on. Petrol is also designed to resist igniting under compression — the reverse of what a diesel wants from its fuel — and that is where the knocking starts. Put those together and the shape of the issue is clear. The harm is done by circulation, not by contact. Where the petrol is only inside the tank, it is an issue of fuel, nothing more. After the pump has been running on that petrol, a mechanical issue has begun: anything shed by a pump that's grinding is carried downstream to the injectors with the fuel. ## Four scenarios our engineers see around Uphill: how bad is petrol in a diesel? Filled up, and not started: nothing beats it. Just the tank has petrol in it, and so the task is draining that tank and rinsing the system where the car stands. This scenario can only really happen at a forecourt: anywhere else, your car got there by being driven. Started for a moment, or only your ignition on. Once primed, the fuel system has pulled petrol from your tank as far as the filter and the fuel lines. That is normally still a straightforward task — a drain, a flush, and your filter dealt with. The pump now worked a few miles on weakened fuel — that is what driving the car does. The work is your tank, the fuel lines, the fuel filter and clean fuel through the whole circuit, and how hard the car was driven matters as much as how far. A school run to Uphill Village Academy is one matter. Any distance on the M5, under 5 miles from Uphill, means the engine has worked hard throughout, and a run to Cardiff, under 15 miles away, is a very different job too. Driven until it complained. Rattling, a lumpy idle, smoke, a throttle that has gone soft. That is the engine telling you its fuel has stopped acting like diesel. Pull up wherever you are — the verge on Saint Nicholas Road, a lay-by, a side street — then leave the vehicle where it is. The drain and flush still come first, and they deal with it: if a car is pulled over quickly, long-term damage is very unusual. ## Petrol in a diesel myths Uphill people hear Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. A bigger tank of the same mix is all you get, because topping up takes out nothing. That advice supposes a diesel fuel system tolerates petrol by percentage. It does not. Myth: "A modern diesel can cope with a bit of petrol." If anything, the opposite. At higher pressure, through more precise parts: that is how a newer diesel moves its fuel, so the lubrication matters for more, not less. This is the one that fools people. Myth: "If it starts and drives, there is no damage done." The motorist of a petrol engine fed diesel usually has no choice but to stop, because it will not run, and the harm stops there. A diesel fed petrol usually starts, ticks over and drives away as if nothing has happened, while the pump wears. Running is not the same as fine. Myth: "Add some two-stroke oil and drive the car home." It is an old workaround for a different issue. It does not put back what petrol has weakened, and that petrol is still inside the tank afterwards. If your engine has been run, part of the petrol is in your filter and the fuel lines, not the tank — and your next start pulls it straight back through the pump. So the myth "drain that tank yourself and you are sorted" does not hold. On top of that, petrol drained into a can by the road is truly hazardous. ## How does petrol in a diesel happen? It is seldom carelessness, and nobody does it on purpose. The petrol nozzle is the smaller of the two and slides into a diesel filler with almost no resistance; a diesel nozzle mostly won't go into a petrol vehicle at all. The forecourt makes it simple, and the mistake runs one way. The moment routine stops matching the vehicle is the moment it occurs. A new car, a hire car or a courtesy car. Two motors on one driveway, one petrol, one diesel. A well-known forecourt with the pumps in a different order. Rushing for a train outside Weston-Super-Mare and fuelling up en route. The first fill-up in a diesel Skoda Octavia after years of driving petrol is exactly the moment it happens. Your hand repeats 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 Uphill: avoiding petrol in a diesel - Green for unleaded and black for diesel is usual in the UK — but not on every forecourt. Go by the label on the pump, not the colour. - In a car you do not know, look inside the flap over the filler or at the cap before your first fill: many motors print the fuel type there. - A coloured fob or a sticker on your diesel's key does more than any amount of intending to remember, in a household with one of each. - Before the nozzle comes off the pump the first time you fill a hired or new vehicle, say "diesel" aloud. Daft, yes, but it does the trick. - Put the phone away. This is an easy mistake to make whilst you are thinking about something else. - Up to a point, a misfuel inhibitor helps: some diesels have a filler built to refuse a petrol nozzle, and aftermarket devices exist for the rest. Treat it as a backstop, then keep checking the pump. - Stop as soon as you realise. Less petrol in the tank makes a thinner mix. It does not change what to do next, which is still not to crank it. ## Uphill: already put petrol in a diesel? Short and simple, then, is the order of things. Leave it unstarted, with the ignition switched off too. Yet on the forecourt, at Shell or anywhere else? Ask the attendants to help you roll it away from the petrol pump. What was put in, roughly how much, and whether it's run: tell us those when you phone 0333 366 0103. If it was AdBlue instead of petrol, say so. That is a different fault — corrosion and deposits rather than lost lubrication — and it has its own page for Uphill. ## Why one petrol in a diesel task around Uphill costs more than another Four different jobs sit behind the four situations above — which is why there is no fair single price. The scenario itself does most of the work of moving your cost. The share matters next, meaning how much of your tank is petrol, followed by the position of the vehicle and whether getting to it is safe for our van. That's why our technicians ask three questions before pricing instead of after: what was put in, how much, and whether it has run. The replies change a range into a straight figure. ## About Uphill itself Uphill is a coastal suburban area in Somerset, situated near the mouth of the River Severn and looking out towards the Bristol Channel. Uphill has a relatively low elevation of around 7 metres above sea level and is close to nearby places such as Uphill Manor and Oldmixon. Uphill is characterised by its predominantly detached housing stock and is located within commuting distance of major cities like Cardiff and Bristol. ## Fuel drain cover in Uphill and across Somerset Uphill rests in the BS postcode area, and the teams that answer petrol in diesel call-outs there work the places around it as well — Uphill Manor, Oldmixon and Clarence Park among them. A forecourt, a supermarket car park, a lay-by or your own driveway are all places we drain, and your vehicle doesn't need to move to us. ## At the pump in Uphill, right now? The best place there is, then — that's where you are. Ring, and leave it switched off.