--- title: AdBlue in a Diesel Tank Johnstown? Read This canonical: https://www.petrolinadieselcar.co.uk/adblue-in-diesel/johnstown-carmarthenshire/ location: Johnstown county: Carmarthenshire latitude: 51.847120 longitude: -4.323370 service: AdBlue in a Diesel Tank updated: 2026-10-17 --- # AdBlue in a Diesel Tank in Johnstown: How It Occurs and How to Stop It If AdBlue is already in your diesel tank, stop reading for a moment: leave the motor and the ignition off and ring 0333 366 0103. A drain plus a thorough flush, carried out just where the vehicle stands around Johnstown, is usually what it takes if found before your engine runs. Not happened yet? Further down, the rest of the page explains the why it takes place and the how to prevent it altogether. ## Why does AdBlue in a diesel motor need its own filler? Plenty of modern diesels around Carmarthen, like those in Johnstown, run on two fluids; the engine takes only the diesel. The exhaust, not your motor, is where AdBlue ends up: dosed into the gas to clean it, from its own tank. Different tanks, separate fillers. Under one flap, next to each other: that's the arrangement on a lot of vehicles. Elsewhere, AdBlue's filler is under the bonnet or in your boot instead. At the petrol pump, your diesel side is topped up constantly. The AdBlue side is filled far less commonly, normally from a bottle, and usually by someone who has to stop and think where it goes. The slip lives in that gap. ## How AdBlue in your diesel tank occurs around Johnstown Carelessness rarely causes it. What does is three things coming up together. First, the warning. Low AdBlue triggers a warning from the car, and letting it run out leads to limp mode — hence a rushed top-up, perhaps before work off Old Llansteffan Road, perhaps at The Poplars Inn on the way home after work. New-to-you cars are next, as well. Hire cars, new motors and company cars put their fillers in new places, and the hand goes for the cap used on the old one. Third, the spout fits: a diesel filler or AdBlue one, it goes in just as readily, and after the tip starts, nothing halts it. Whether it occurs in Pibwrlwyd or the middle of Johnstown, it is the same few seconds. ## How to tell the AdBlue filler from the diesel one Before you pour anything, whether on a driveway in Travellers Rest or a forecourt in Johnstown, check these. They take a few seconds. - Where it sits can mislead; the cap does not. AdBlue caps tend to be blue or carry the word "AdBlue" — diesel caps normally don't. - Check the size: the smaller filler neck is, on plenty of cars, the AdBlue one. - Look inside your fuel flap: many motors carry a label there saying which fuel goes where. - The handbook. If the filler is not by the diesel cap, it's in the boot or under the bonnet, and the handbook says which. - The person who drove the vehicle last. On a hire or company car collected from somewhere like the car park outside Carmarthen, ask before you leave, not when the light comes on. ## Keeping AdBlue out of your diesel tank when you top up Wherever around Carmarthenshire the light comes on, this is a routine for the day. - Not in a rush on the side of Porth y Plas, not on a slope, not with the motor running: park and switch off properly. - Find the AdBlue filler, read the cap, and speak the name "AdBlue" aloud while unscrewing it. It seems daft. It works. - If both sit under one flap, check the diesel cap is still closed before you lift the bottle — and leave it on. - Finish when your tank fills or the bottle runs dry; until then, tip gently using the own spout. - Shut the cap, and look once more — confirm your diesel cap stayed closed throughout. After that, start the car. If at step two or three you find you have already poured into the diesel side, stop there. Do not go on to stage five. ## Put AdBlue in the diesel tank in Johnstown already? What follows is a short order of things, beginning with not starting your engine. Keep your ignition off as well, since on many diesels it by itself starts the fuel pump. Don't top up with diesel to dilute it: AdBlue does not mix with diesel, it sinks to the bottom of that tank, where your fuel is pulled from. If you are on a forecourt, whether it's the Johnstown Filling Station or the Tesco, ask the attendants to help roll the car away from the pump. Your own driveway in Johnstown is the place it stays. If the engine has already run, stop as soon as it is safe then switch off. The next junction means the place to come off when you are on the M4, under 15 miles from Johnstown. A short hop across Johnstown is a smaller job than a run towards Swansea, under 25 miles away, so tell us roughly how far it went. ## Our arrival around Johnstown, and what occurs next The van comes to your car anywhere it has come to rest — your own drive, beside Plas Ystrad Mansion, or by the local primary school. Both the work and our quote rest on three replies — which fluid, which amount, and if it's run — so our technicians ask. No one heads out until you have had our quote by phone. Next: draining, then a full flush of the entire 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 that matters more here than with petrol. The fuel filter is flushed, or replaced where it needs to be; fresh diesel goes in; and the car is tested. Before we go, our engineers fire it up and check that it's running smoothly. With pumps fine on a working forecourt and quiet enough to use outside a house at night, most jobs in which your motor hasn't run need about half an hour after our engineers arrive. No money in advance; you settle up that day. Afterwards, a VAT invoice and a report from the engineer go to you for your insurer. Before we get there, have a look at your policy; many carry cover for misfuelling. ## About Johnstown and where it is Johnstown is a suburban area in Carmarthenshire, situated on the riverside at a low elevation of around 12 metres. Johnstown lies near several small communities, including Pibwrlwyd, Pen-sarn, and Llanllwch, and is within commuting distance of Swansea, which is approximately 23 miles away. Johnstown has a population of around 1505 people and is characterised by predominantly detached housing. ## AdBlue drains across Carmarthenshire, Johnstown included Johnstown is a residential suburb, and the vans that cover it also work the towns around it, Pen-sarn and Llanllwch among them, across the SA postcode area. Quote a postcode beginning SA31 3, and our van gets there quickest. The car stays put. A driveway, a lay-by on the way to Athletic Park, a side street close to Carmarthen Harriers Stadium: our technicians drain the vehicle where it is. If you're near a boundary, or somewhere hard to explain like the back of Carmarthen Leisure Centre, ring and ask rather than assuming. ## Johnstown drivers: the short version Read the cap before you pour. If AdBlue has gone in the diesel tank regardless, leave the vehicle off and ring 0333 366 0103. Petrol in Diesel empties it where it stands, anywhere across Carmarthenshire.