--- title: March: Petrol in a Diesel Car, Explained canonical: https://www.petrolinadieselcar.co.uk/petrol-in-diesel/march-cambridgeshire/ location: March county: Cambridgeshire latitude: 52.547490 longitude: 0.087330 service: Petrol in a Diesel Car updated: 2026-10-27 --- # March: Petrol in a Diesel Car? How Worried to Be If it has not been started, you can worry far less than you likely are. Until your ignition primes the pump, your starter cranks, or the car is driven, petrol in a diesel tank simply rests there and does no harm. Which means the honest reply to the first March query — "have I ruined it?" — normally no. Keep it like that: leave your engine off then ring Petrol in Diesel. The remainder of this page sets out what petrol actually does to a diesel, how to tell how far it has got, and how to make sure it doesn't happen to you again. ## Inside your engine: what petrol in a diesel does Diesel does two tasks on its way through a motor. It combusts, and before it combusts it protects. Very fine gaps are built into the injectors and the high-pressure pump, and just the diesel flowing through stops those surfaces grinding together. The second task petrol doesn't do at all, and the first it does poorly. It's thinner than diesel and takes away the lubrication the fuel system hinges on, so a pump running on a petrol mixture is a pump wearing itself. And petrol is made to resist igniting under compression, which is the opposite of what a diesel needs from its fuel. That is where the clattering comes from. Seen together, they show the shape the problem takes. The harm is done by movement, not by contact. Any tank with petrol in it is a fuel fault. A pump that has been labouring on that petrol is the beginning of a mechanical one, and whatever a worn pump sheds travels on with your fuel to the injectors further on. ## How serious is petrol in a diesel? Four scenarios our engineers see in March Fuelled, and not started: nothing beats it. At a forecourt, and truly only there, the petrol is still confined to that tank — since everywhere else your car was driven to get to it. The job is draining and flushing on the spot. Ignition on, or started for a moment. Petrol has left that tank and reached your filter and the lines, because the system has been bled. Usually little more than emptying, rinsing and sorting the fuel filter, so still easy. A couple of miles driven, and the pump has spent every one of them labouring on weakened fuel. How hard the vehicle was driven matters as much as how far, and the work covers that tank, the fuel lines, the filter and fresh fuel through the whole system. Driving the children to Burrowmoor Primary Academy is one kind of trip. Driving as far as Ely, under 15 miles away, makes a very different task — as does any distance on the A1(M), under 25 miles from March, with the motor labouring hard all the way. Clattering, an uneven idle, smoke, a throttle gone soft: driven till it complained. That's the engine telling you its fuel no longer is acting like diesel. Whether it is the verge on Burrowmoor Road, a lay-by or a side road, stop where you are and leave it. Permanent damage is very uncommon if a car is pulled over early, and the drain and flush-through that still come first take care of it. ## Stories March people hear about petrol in a diesel Myth: "Fill it the rest of the way with diesel and it'll be fine." It will not. Nothing is removed by topping up — you are left with a bigger tank, still the same mixture. A diesel fuel system does not tolerate petrol by percentage in the way that advice assumes. If anything, the opposite is true. Myth: "A modern diesel can cope with a bit of petrol." Protection matters more on newer diesels, not less, because their fuel passes through more precise components at higher pressure. One myth that catches people off guard: if it starts and drives, it must be unharmed. A petrol motor fed diesel normally won't run, so the motorist stops and the damage stops with them. Feed petrol to a diesel and it usually starts, ticks over and pulls away as if nothing has happened — all the while its pump wears. Fine and running are not the same at all. An old workaround for a different issue lies behind this one. Myth: "Add some two-stroke oil and drive the car home." It doesn't put back what petrol has diluted, and that petrol is still in the tank afterwards. "Drain it yourself and you're sorted" — a myth, because after it's been running some petrol lies in the filter and lines, ready to go straight back through the pump on your next start. It is also truly risky to drain petrol into a can at the kerbside. ## How it happens: petrol in a diesel On purpose? Never. Through carelessness? Rarely, if ever. The petrol nozzle is the narrower of the two and slips into a diesel filler with almost no resistance; a diesel nozzle mostly will not go into a petrol motor at all. The forecourt makes it easy, and the slip runs one way. The moment routine stops matching the car is the moment it occurs. A new vehicle, a hire car or a courtesy car. A household with one petrol and one diesel on the drive. A well-known forecourt with the pumps in a different order. Fuelling up in a rush en route to the nearest station, with a train to catch. A new-to-you diesel Volkswagen Golf, its first fuelling, and a motorist accustomed to petrol: precisely when it happens. With rain, a call arriving, or a car full of children to deal with, your hand just does what it always has. ## Preventing petrol in a diesel next time you fill up in March - Check the petrol pump, not the colour. In the UK unleaded handles are usually green and diesel black, yet not on each forecourt. The label is what matters. - Plenty of motors state the fuel type inside your filler flap or on the cap, and so check it on your first fill in any motor you don't know. - A coloured fob or a sticker on the diesel's key does more than any amount of meaning to remember, for a home with one of each. - Before the nozzle comes off the pump the first time you fill a hired or new car, say "diesel" out loud. Daft, yes, but it does the trick. - Mistakes like this are easy to make while your mind is on something else, so the phone goes away. - Up to a point, a misfuel inhibitor helps: some diesels have a filler designed to refuse a petrol nozzle, and aftermarket devices exist for the rest. Treat it as a backstop, then keep reading the pump. - Spotting it halfway? Stop there and then. A weaker mixture follows from less petrol in the tank, but your next step stays the same: do not crank it. ## March: already put petrol in a diesel? Then, there is only a short order of things. Starting it is out, and so is turning on the ignition. Ask the staff to help you push it clear of the pump if you're still at the forecourt, whether that's BP or anywhere else. Call 0333 366 0103 next, with three facts — your fuel, the approximate volume, and whether it's run. Say so if it was AdBlue rather than petrol: it's a different problem, with its own page for March, because AdBlue brings corrosion and deposits instead of lost lubrication. ## March petrol in a diesel jobs: why one costs more than another There is no fair single price for this, because the four situations above are four different jobs. Which of them you are in is mostly what shifts the cost. Two things follow that: the petrol that went in as a share of what that tank holds, then the spot the vehicle is in and whether a technician can get to it safely. What was put in, how much, and whether it has run — three questions our engineers ask before costing, not after, for precisely that reason. Those answers change a range into a straight figure. ## About March itself March is a town situated on the banks of the River Nene in Cambridgeshire, with a low elevation of around 5 metres. March is located near several smaller settlements, including Little London, Badgeney, and Town End, and is close to the city of Ely. March has a population of approximately 18,120 people and is characterised by a predominance of detached housing. March is also within commuting distance of London, being around 72 miles from the capital. ## March and Cambridgeshire: where our fuel drain cover reaches March rests in the PE postcode area, and the vans that answer petrol in diesel jobs there work the spots near it as well — Little London, Badgeney and Town End among them. You need not bring the vehicle to us. Forecourts, supermarket car parks, lay-bys and your own driveway are all locations where we work. ## Still at the pump in March? Then you are in the best position there is. Keep it off. Phone.