--- title: Explained: AdBlue in a Diesel Tank Llanlleian-wen canonical: https://www.petrolinadieselcar.co.uk/adblue-in-diesel/llanlleian-wen-swansea/ location: Llanlleian-wen county: Swansea latitude: 51.677440 longitude: -3.916760 service: AdBlue in a Diesel Tank updated: 2026-10-17 --- # Llanlleian-wen: How Does AdBlue End Up in a Diesel Tank, and How Do You Avoid It? Leave your engine and ignition off and phone 0333 366 0103 now — reading can wait when AdBlue is already in your diesel tank. A drain and a thorough flush, done right where the vehicle sits in Llanlleian-wen, is normally all it takes when caught before your engine runs. Nothing happened yet? Further down, the rest of the page explains the why it occurs and the ways to prevent it altogether. ## AdBlue in a diesel vehicle: two tanks, two fillers Many newer diesels on the roads round Llanlleian-wen and Cwmrhydyceirw carry two liquids, not one. Diesel goes to your motor. Its own tank holds it, and from there it goes to your exhaust, and there a spray cleans the gas. There's a filler for each tank. On a lot of cars the two sit side by side under the same flap; on others the AdBlue filler is in your boot or under the bonnet. Topping up the diesel side at the pump goes on constantly. The AdBlue side is topped up far less regularly, usually from a bottle, and normally by somebody who has to stop and think where it goes. Mistakes happen in that gap between the two. ## AdBlue in the diesel tank in Llanlleian-wen: how it takes place It's seldom carelessness. Three things tend to line up. The warning comes first. As AdBlue runs low the car tells you, and if it runs out completely, the car goes into limp mode. So the top-up is done in a hurry: on a drive off Glyncollen Crescent before work, or in the car park at Deer's Leap on the way home. The old car's cap is where your hand reaches — yet a rental car, a new car or a company car keeps the fillers elsewhere. That is the second thing: a strange motor. A spout-topped bottle finds no resistance at a diesel filler no more than at an AdBlue one. And so the pour, after started, keeps on. Whether it takes place in Ynysforgan or the middle of Llanlleian-wen, it is the same few seconds. ## Which filler is for AdBlue, and which for diesel? Be it a Llanlleian-wen forecourt or a driveway over in Tircanol, take a couple of seconds on these before anything goes in. - Read the cap rather than going by position: AdBlue caps are commonly blue or marked "AdBlue", and diesel caps usually aren't. - On plenty of vehicles, size tells: AdBlue gets the smaller filler neck. - A label inside your fuel flap often says which fuel goes where, on many motors. Check for it. - The handbook shows where it lives if the filler isn't next to the diesel cap: your boot, or under the bonnet. - Whoever had it before knows. Ask when you collect a hire car or company car — at Llansamlet's car park, say — not once the warning appears. ## How to top up without AdBlue in your diesel tank The day the light comes on, anywhere in Swansea, use this routine. - Park then switch off. Not on a slope, not with the engine running, and not in a rush on the side of Gwern Fadog Road. - Say "AdBlue" out loud as you unscrew the cap, once finding the AdBlue filler and reading it. Daft, yes, but it does the trick. - The diesel cap remains on. Where both sit under a flap, make sure it's closed before the bottle comes up. - Gently is best, through the bottle's own spout, till it is full or the bottle is empty. - Close the cap and check again. Make sure your diesel cap was never opened. Only then start the vehicle. Discover at the second or third stage that the bottle went into the wrong filler? That is where you stop. Don't go on to stage five. ## AdBlue in the diesel tank already, in Llanlleian-wen? Short order, then. Top of it: the motor stays unstarted. On plenty of diesels your ignition alone runs the fuel pump, and so do not switch the car on. Don't top up with diesel to dilute it: AdBlue does not mix with diesel, it sinks to the bottom of the tank, where the fuel is drawn from. At a forecourt — Asda, BP or another — the staff will usually help push the vehicle away, if you ask. If you are on your own drive around Llanlleian-wen, leave the car where it stands. Stop as soon as it is safe then switch off, if your motor has already run. Leave the M4 — under a mile out of Llanlleian-wen — at the next exit. Mileage matters — a quick hop across Llanlleian-wen makes a smaller job than driving under 5 miles to Swansea — so say about how far it went. ## Our arrival around Llanlleian-wen, and what takes place next By the local primary school, near Morriston Leisure Centre or on your own driveway: wherever the vehicle has stopped, we come to it. The replies determine the work and the price, and so we ask what got in, about how much, and whether it has run. That price comes on the call, ahead of any van leaving. Emptying the tank comes next, then a full flush of the fuel system. More than with petrol, it counts here: crystals form, certain metals are attacked, and nothing clears out unaided, however long it sits. Testing is last: before that, fresh diesel goes in, and the filter is cleaned or changed as needed. Before we go, our engineers fire it up and confirm that it is running properly. If the engine hasn't run, the majority of jobs take about half an hour once we are there, using pumps that are fine on a busy forecourt and quiet enough to use outside a house after dark. You pay on the day, with nothing upfront, and get a VAT invoice and an engineer report for your insurer. Wrong-fuel cover is included in plenty of insurance policies — so make use of the wait to check yours. ## About Llanlleian-wen, briefly Llanlleian-wen is a suburban area situated on the riverside in Swansea, with an elevation of 29 metres above sea level. Llanlleian-wen lies approximately 4 miles from Swansea city centre and is surrounded by nearby places such as Ynysforgan and Pen-rhiw-forgan. Llanlleian-wen has a population of around 3305 people and predominantly features semi-detached housing. Llanlleian-wen is located in a region with a mix of urban and natural environments, given its proximity to the river and the city of Swansea. ## AdBlue drains around Llanlleian-wen and across Swansea Being a residential suburb, Llanlleian-wen shares its vans surrounding areas — Pen-rhiw-forgan, Cwm-felin-fach — all the way through SA postcodes and the surrounding area around them. Our van reaches you fastest with a postcode starting SA6 6. The vehicle remains where it is. A drive, a lay-by on the way to Gwern-Fadog Plantation, a side street near Morriston Library: our technicians drain the car where it is. If you're near a border, or somewhere hard to describe like the back of Seion Newydd Chapel, ring and ask rather than guessing. ## In short, for Llanlleian-wen motorists Read the cap before you tip. If AdBlue has gone in the diesel tank all the same, leave the vehicle off then ring 0333 366 0103. Petrol in Diesel empties it where it stands, anywhere around Swansea.