--- title: AdBlue in a Diesel Tank Upper Common: Explained canonical: https://www.petrolinadieselcar.co.uk/adblue-in-diesel/upper-common-monmouthshire/ location: Upper Common county: Monmouthshire latitude: 51.829480 longitude: -3.093060 service: AdBlue in a Diesel Tank updated: 2026-10-14 --- # How It Occurs and How to Prevent It: AdBlue in a Diesel Tank in Upper Common Pause reading for a moment when the diesel tank already holds AdBlue in it: ignition off, engine off, then ring 0333 366 0103. In Upper Common, finding it before your motor runs normally leaves draining and a full flush where it stands. Not happened yet? Below, the page explains the why it happens and the how to prevent it altogether. ## AdBlue in a diesel vehicle: two tanks, two fillers Many current diesels on the roads around Upper Common and Glangrwyney carry two liquids, not one. Diesel goes to your engine. AdBlue's own tank keeps it, and from there it is sent to the exhaust, and there a spray treats the fumes. Every tank comes with a filler of its own. Under one flap, next to each other: that's the arrangement on a lot of motors. Elsewhere, AdBlue's filler is under the bonnet or in the boot instead. At the pump, the diesel side is topped up all the time. Someone who has to stop and think where it goes usually fills the AdBlue side, from a bottle, and much less frequently. It's in the gap that the mistake lives. ## How does AdBlue in the diesel tank take place around Upper Common? Carelessness rarely explains it. Instead is three things coming up together. The warning comes first. As AdBlue runs low the vehicle tells you, and if it runs out completely, your vehicle goes into limp mode. So the top-up is done in a hurry: on a drive off Common Road before work, or in the car park outside Corn Exchange on the way home. Next, the hand goes for the cap it would have used on the old vehicle — since a rental car, a new car or a company car places the fillers where your last one didn't. A spout-topped bottle finds no resistance at a diesel filler no more than at an AdBlue one. So the tip, once begun, keeps on. Lower Common or the heart of Upper Common: it takes the same few seconds either way. ## Which filler is for AdBlue, and which for diesel? Before you tip anything, whether on a driveway in Twyn Wenallt or a forecourt around Upper Common, check these. They take a few seconds. - The cap. The AdBlue cap is commonly blue, or marked "AdBlue". Your diesel cap usually isn't. Read it rather than going by position. - Check the size: the smaller neck is, on plenty of cars, the AdBlue one. - A label inside the fuel flap often says which fuel goes where, on many cars. Check for it. - Can't find it beside your diesel inlet? In that case check below the bonnet or inside your boot — the handbook says which. - Check with the person who drove it last — before you leave, not when the light comes on — when you collect a hire or company car from somewhere like the car park outside Abergavenny. ## Topping up AdBlue without it reaching the diesel tank A routine for the day the light comes on, wherever in Monmouthshire that is. - Pull in on level, motor off, with time in hand — never rushing on the side of Fairhome. - Silly as it sounds, saying "AdBlue" aloud as you unscrew the cap does the trick — once you've found the filler and read the cap. - If both sit under one flap, check the diesel cap is still closed before you lift the bottle — and leave the vehicle on. - Stop once the tank is topped up or the bottle is empty; until then, pour slowly through the own spout. - Before you start the vehicle, shut the cap and check again that the diesel cap never opened off. If at stage two or three you find you have already poured into your diesel side, stop there. Skip step five entirely. ## Already put AdBlue in your diesel tank in Upper Common? Then the order of things is short. Do not start the motor. Leave your ignition off too, because on many diesels it by itself runs your fuel pump. Diluting it with more diesel won't work, because AdBlue settles to the bottom instead of mixing — and that is where the fuel is drawn from. The attendants at Gulf, BP or another forecourt will usually lend a hand to push your car away when asked. On your own drive in Upper Common? Then the vehicle stays put. Already run? Pull over once it's safe, then switch off. The next junction is where to leave if you're on the M4, under 25 miles from Upper Common. A short hop across Upper Common is a smaller job than a run towards Newport, under 25 miles away, so tell us roughly how far it went. ## When we get there in Upper Common, what happens? Our engineers come to the vehicle wherever it has stopped, whether that's outside the local primary school, near Gilwern Community Hub or on your own drive. Both the work and our price rest on three answers — which liquid, which amount, and whether it's run — so we ask. You get that quote on the phone, before anyone sets off. Emptying your tank comes next, then a thorough flush of the system. AdBlue crystallises and is corrosive to some of the metals in a fuel system, so it does not wash out on its own — which is why the flush matters more here than with petrol. The filter flushed or, where it must be, swapped; clean diesel in; then a test of your car. Before leaving, we start the engine and make sure that it is running correctly. Unstarted vehicles usually need a half-hour job from the moment we arrive. The equipment is safe on a busy filling station, and quiet enough for a driveway late at night. You pay on the day, with nothing upfront, and get a VAT invoice and an engineer report for your insurer. It is worth looking at your insurance while we travel to you: misfuelling cover comes with many policies. ## About Upper Common itself Upper Common is a suburban area located on the riverside in Monmouthshire, Wales, with a mix of detached housing and a population of around 2235 residents. Upper Common sits at an elevation of 82 metres, near the communities of Lower Common and Gilwern, and is approximately 17 miles from Newport. Upper Common is part of a wider area that includes nearby Pen-y-bont and other small settlements along the river. Upper Common has a relatively low elevation compared to other areas in the region, which are often hillier and more rural. ## Upper Common and Monmouthshire: AdBlue drains across the area Upper Common is a residential suburb, and our teams that cover it also work the places near it, Gilwern and Pen-y-bont among them, across the NP postcode area. Quickest of all: give a NP7 0 postcode for the van. There's no need to shift the vehicle. A drive, a lay-by on the way to Garden of Remembrance, a side street near Garden of Remembrance: our technicians drain it where it sits. Assuming won't help at the back of Gilwern War Memorial, close to a border, or anywhere awkward to pin down; phone and check. ## The short version for Upper Common drivers Before you tip, read the cap. Still AdBlue in your diesel tank? Petrol in Diesel will empty it wherever it is, anywhere around Monmouthshire: switch the car off and ring 0333 366 0103.