--- title: Explained: AdBlue in a Diesel Tank Black Tar canonical: https://www.petrolinadieselcar.co.uk/adblue-in-diesel/black-tar-pembrokeshire/ location: Black Tar county: Pembrokeshire latitude: 51.748220 longitude: -4.905930 service: AdBlue in a Diesel Tank updated: 2026-10-06 --- # Avoiding AdBlue in a Diesel Tank in Black Tar: Why It Occurs If AdBlue is already in your diesel tank, stop reading for a moment: leave your engine and your ignition off and ring 0333 366 0103. A drain plus a thorough flush, done just where the vehicle stands in Black Tar, is usually what it takes if caught before the engine runs. If you are reading before it has happened, the rest of this page is about why it occurs and how to make sure it does not. ## AdBlue in a diesel vehicle: two tanks, two fillers Many modern diesels around Port Lion, like those in Black Tar, carry on two liquids; your engine gets only the diesel. Kept in a tank of its own, AdBlue is fed into the exhaust gas to clean it. Separate tanks, different fillers. Under one flap, next to each other: that is the arrangement on a lot of cars. On others, AdBlue's filler sits beneath the bonnet or in your boot instead. At the pump, your diesel side gets filled all the time. Seldom filled, AdBlue normally goes in out of a bottle, poured by someone who has to stop and think which cap to use. The slip lives in that gap. ## How does AdBlue in your diesel tank happen around Black Tar? It is seldom carelessness. Three things tend to line up. First, the warning. Low AdBlue triggers a warning from the car, and letting it run out means limp mode — so a hurried top-up, maybe before work off Glan Hafan, or at The Cottage Inn on the way home after work. Then your car is strange. A hire car, a new vehicle 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. A spout-topped bottle finds no obstacle at a diesel filler no more than at an AdBlue one. And so the tip, after begun, carries on. Llangwm or the middle of Black Tar: it takes the same few seconds in both. ## The AdBlue filler and your diesel filler: telling them apart Be it a Black Tar forecourt or a driveway over in Deerland, spend a few seconds over these before any goes in. - Check the cap rather than going by position: AdBlue caps are often blue or marked "AdBlue", and diesel caps normally aren't. - Check the size: the smaller neck is, on plenty of motors, the AdBlue one. - A label inside the fuel flap often shows which fuel goes where, on many vehicles. Check for it. - Can't see it beside your diesel filler? In that case check beneath the bonnet or in the boot — the handbook says where. - Ask the person who drove it last — before you leave, not when the light comes on — if you collect a hire or company car from somewhere like the car park outside Johnston. ## Keeping AdBlue out of the diesel tank when you top up When the light comes on, anywhere around Pembrokeshire, follow this routine. - Turn off after you park — flat ground, motor off, and never rushed by Rectory Close at the roadside. - Find the AdBlue filler and read the cap. Say "AdBlue" out loud as you unscrew it. It sounds silly and it works. - Leave the diesel cap on. If both sit under one flap, check the diesel cap is still closed before you lift the bottle. - Pour slowly, using the bottle's own spout. Stop when it's full or when the bottle is empty. - Close the cap, then look again — making sure your diesel cap remained shut the whole time. Only then, start the vehicle. Spot at stage two or three that it has already gone into the diesel side? Then stop just there. Step five is off limits. ## Black Tar: already put AdBlue in the diesel tank? What follows is a short order of things, starting with no starting your engine. Do not switch the ignition on; on many diesels that alone runs the fuel pump. 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. Ask the staff to help push the car clear of the petrol pump if you're at a forecourt — the Texaco, the Asda or anywhere else. At home around Black Tar? So the car stays where it is. Already run? Pull over once it is sensible, then switch off. Black Tar sits under 50 miles from the M4; on it, use the first junction. Tell us roughly how far it went: a run towards St Davids, under 25 miles away, is a bigger job than a short hop across Black Tar. ## Black Tar: what takes place when we turn up Outside the local primary school, close to Adeilad Clwb Rygbi Llangwm or on your own driveway: wherever the car has stopped, our engineers come to it. Both the work and our quote rest on three answers — what liquid, which amount, and whether it's run — so we ask. That price is given on the call, ahead of any van leaving. After that: a drain, then a full flush of the whole system. With AdBlue that matters more than with petrol: it crystallises and is corrosive to some of the metals in a fuel system, so it doesn't wash out on its own. A test comes last: before that, clean diesel goes in, and your filter is flushed or changed if necessary. Before we go, our technicians fire it up and make sure that it's running smoothly. Unrun cars usually mean a half-hour job from arrival. The equipment is safe on a live forecourt, 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. Misfuelling cover is included in plenty of insurance policies — and so use the wait to check yours. ## About Black Tar, briefly Black Tar is a small coastal locality in Pembrokeshire, situated near the villages of Llangwm and Guilford, with detached housing being the predominant type of accommodation. Black Tar sits at a low elevation of around 12 metres, close to the sea, and is located approximately 17.9 miles from St Davids. Black Tar is part of a wider area of scattered settlements and rural landscapes in western Wales. Black Tar has a small population of around 500 people. ## Black Tar and Pembrokeshire: AdBlue drains across the area As a coastal area, Black Tar has the same vans as surrounding areas — Guildford, Guilford — right through SA postcodes and the wider area beyond. A postcode starting SA62 4 gets the van to you fastest. The car doesn't need to move. Wherever it stands — beside The Hanging Stone, in a lay-by en route to Sams Wood, on a drive — that is where it gets emptied. If you're near a border, or somewhere hard to explain like the back of Benton Castle, ring and ask rather than assuming. ## For Black Tar motorists, the short version Tip nothing until you've read the cap. AdBlue in the diesel tank regardless? Leave it off and phone 0333 366 0103; Petrol in Diesel empties it on the spot, throughout Pembrokeshire.