--- title: Waunfawr: AdBlue in a Diesel Tank, Explained canonical: https://www.petrolinadieselcar.co.uk/adblue-in-diesel/waunfawr-gwynedd/ location: Waunfawr county: Gwynedd latitude: 53.112070 longitude: -4.208070 service: AdBlue in a Diesel Tank updated: 2026-10-21 --- # Why It Happens and How to Avoid It: AdBlue in a Diesel Tank in Waunfawr If AdBlue is already in your diesel tank, stop reading for a moment: leave your engine and your ignition off then call 0333 366 0103. In Waunfawr, catching it before your engine turns normally leaves draining and a full flush on the spot. Here in advance? In that case what follows covers how it happens and how to stop it ever happening. ## AdBlue in a diesel vehicle, and its separate tank Diesel goes to the engine — but plenty of newer diesels seen around Waunfawr and Betws Garmon hold a second liquid too. The exhaust, not your motor, is where AdBlue goes: sprayed into the gas to clean it, from its own tank. Every tank comes with a filler of its own. Many of cars have a single flap for the two, while some move the AdBlue filler to your boot or under the bonnet. Topping up your diesel side at the pump goes on constantly. Much less commonly, the AdBlue side is topped up — mostly from a bottle, by a person thinking about where it goes. That gap is where the error lives. ## How does AdBlue in your diesel tank take place around Waunfawr? Three things tend to line up, and carelessness is seldom one of them. Haste comes from the warning. Your car tells you as AdBlue runs low, and a dry tank puts it into limp mode — so the top-up gets done in a rush, before work on a drive off Bryn Goleu, or on the way home in the car park at Snowdonia Parc. Then the vehicle is unfamiliar. A hire car, a new car or a company car puts the fillers where your last one didn't, and the hand reaches for the cap it would have used on the old one. Third, the spout goes in: a diesel filler or AdBlue filler, it slides in just as easily, and once the pour starts, no part halts it. It takes seconds, whether out in Croesywaun or bang in the centre of Waunfawr. ## How to tell the AdBlue filler from the diesel one Check these first, on a forecourt around Waunfawr or a driveway out in Tan-y-coed. Seconds, no more. - Where it sits can mislead; the cap does not. AdBlue caps are often blue or bear the word "AdBlue" — diesel caps usually do not. - On plenty of vehicles, the size gives it away: AdBlue gets the smaller filler neck. - The flap. Look inside the fuel flap for a label. Many motors say there which fuel goes where. - In your boot or under the bonnet: that's where your filler is if it's not by the diesel cap, and the handbook says which. - The person who drove it last. On a hire or company car collected from somewhere like the car park at Llanfairpwll, ask before you leave, not when the light comes on. ## AdBlue top-ups that never reach the diesel tank Wherever around Gwynedd the light comes on, this is a routine for that day. - Park then switch off. Not on a slope, not with your motor running, and not in a rush on the side of Stad Ty Hen. - Locate the AdBlue filler, check the cap, and say the word "AdBlue" out loud as unscrewing it. It seems silly. It works. - Both behind one flap? So confirm the cap on your diesel side is still shut ahead of raising the bottle. - Slowly is best, through the bottle's own spout, till it is full or the bottle is empty. - Close the cap and check a second time. Make sure the diesel cap was never opened. Only then start the vehicle. If at step two or three you find you have already poured into the diesel side, stop there. Don't carry on to step five. ## Already put AdBlue in the diesel tank in Waunfawr? Then the order of things is short. Do not start your motor. Don't switch the ignition on; on plenty of diesels that alone runs the fuel pump. Thinning it with more diesel won't work, since AdBlue settles to the base rather than blending — and that's where the fuel is drawn from. At a forecourt — Shell, Essar or any other — the staff will usually help push the car clear, if you ask. Leave it where it is if you are on your own driveway in Waunfawr. If the engine has already run, stop as soon as it is safe then switch off. Leave the Moreton Spur — under 50 miles out of Waunfawr — at the next junction. A short hop across Waunfawr is a smaller job than a run towards Bangor, under 10 miles away, so tell us about how far it went. ## What takes place when our engineers arrive around Waunfawr We come to the vehicle wherever it has stopped, whether that's outside the local primary school, close to Former ROC Nuclear Monitoring Post 1959-69 or on your own drive. Both the work and the price rest on three answers — what fluid, which amount, and whether it has run — so we ask. Nobody sets off before you've heard our quote by phone. Next: a drain, then a full flush of the whole system. AdBlue crystallises and is corrosive to some of the metals in a fuel system, and so it does not wash out on its own — which is why the flush matters more with AdBlue than with petrol. Once your filter has been cleaned — or replaced, if needed — clean diesel is added, and then your vehicle gets tested. After that our engineers start it and make sure it runs correctly before we leave. Unrun cars usually need a half-hour visit from the moment we arrive. The equipment is safe on a live forecourt, and quiet enough for a residential street after dark. No money upfront; you settle up on the day. Afterwards, a VAT invoice and the report from the engineer are handed to you for your insurer. Before we get there, have a look at your insurance documents; many carry cover for misfuelling. ## About Waunfawr Waunfawr is a small village in Gwynedd, situated on the banks of a river at an elevation of 153 metres. Waunfawr lies near the villages of Croesywaun, Groeslon, and Ceunant, and is approximately 8.7 miles from Bangor. Waunfawr has a population of around 654 people, predominantly living in semi-detached houses. Waunfawr is located in northwest Wales, about 204.9 miles from London. ## AdBlue drains around Waunfawr, and Gwynedd beyond Throughout LL postcodes, the teams covering Waunfawr — a village — work the nearby spots too, Ceunant and Groeslon included. Quickest of all: quote a LL55 4 postcode to our van. Your car doesn't need to shift. Anywhere it stands — near St Garmon, in a layby en route to Y Bicell, at home — that is where it is cleared. Assuming won't help behind Hut Circles (Cae Hen), close to a border, or somewhere awkward to pin down; phone and check. ## Waunfawr motorists: the short version Read the cap before you tip. Even so AdBlue in the diesel tank? Petrol in Diesel can empty it where it stands, wherever around Gwynedd: switch the car off then call 0333 366 0103.