--- title: AdBlue in a Diesel Tank Johnston? Read This canonical: https://www.petrolinadieselcar.co.uk/adblue-in-diesel/johnston-pembrokeshire/ location: Johnston county: Pembrokeshire latitude: 51.754720 longitude: -4.997400 service: AdBlue in a Diesel Tank updated: 2026-10-24 --- # Preventing AdBlue in a Diesel Tank in Johnston: Why It Happens Stop here a minute when your diesel tank already holds AdBlue in it: ignition off, motor off, and call 0333 366 0103. A drain plus a full flush, carried out just where your car sits around Johnston, is usually what it needs when caught before your engine runs. The remainder of this page covers why it takes place and how to ensure it doesn't — handy if you are reading before it has happened. ## Two fillers, two tanks: AdBlue in a diesel motor Many current diesels on the roads around Johnston and Tiers Cross carry two liquids, not one. Diesel goes to your motor. Kept in a tank of its own, AdBlue is sprayed into your exhaust stream and cleans it. Every tank has one filler of its own. Other motors put the AdBlue filler in the boot or under the bonnet; a lot of others have both side by side behind one flap. The diesel side is filled at the pump all the time. Seldom topped up, AdBlue normally goes in out of a bottle, poured by a driver who has to stop and think which cap it needs. That gap is where the mistake lives. ## AdBlue in your diesel tank in Johnston: how it happens Three things tend to come together, and carelessness is seldom one of them. The warning comes first. As AdBlue runs low the car tells you, and if it runs out completely, the car drops into limp mode. So the top-up is done in a hurry: on a drive off Milford Road before work, or in the car park outside The Railway Inn on the way home. New-to-you cars come next, too. Hire cars, new motors and company cars put their fillers in new places, and the hand reaches for the cap used on the old one. Lastly, the bottle fits: a diesel filler or AdBlue one, it goes in as readily, and once the pour begins, nothing stops it. It's seconds, whether in Pope Hill or bang in the centre of Johnston. ## Which filler is for AdBlue, and which for diesel? Before you pour anything, whether on a driveway in Middle Hill or a forecourt around Johnston, check these. They take a few seconds. - Colour and lettering: an AdBlue cap is often blue, or says "AdBlue", where a diesel cap usually doesn't. Trust the cap, not where it sits. - On many motors, size gives it away: AdBlue has the smaller filler neck. - Open the filler flap and check for a label — many motors mark which belongs in which filler right there. - In the boot or under the bonnet: that's where the filler is if it is not by your diesel cap, and the handbook tells you which. - Ask the person who drove it last — before you leave, not when the light comes on — when you pick up a hire or company car from somewhere like the car park at the nearest station. ## Topping up AdBlue without it reaching your diesel tank Wherever in Pembrokeshire the light comes on, this is a routine for that day. - Turn off once parked — level ground, motor stopped, and never in a rush by The Crescent at the roadside. - Locate the AdBlue filler, read the cap, and say the word "AdBlue" out loud as you unscrew it. It seems silly. It works. - Both under a single flap? So make sure the cap on the diesel side is still closed before raising the bottle. - Finish once that tank fills or the bottle runs dry; until then, pour gently through its own spout. - Only after that, start the car: close the cap, check once more, and make sure the diesel cap was never opened. Discover at the second or third step that AdBlue went in the wrong filler? That is where you stop. Don't carry on to step five. ## Already put AdBlue in the diesel tank around Johnston? What follows is a short order of things, beginning with not starting the motor. Leave the ignition off as well, since on plenty of diesels it alone runs the fuel pump. Do not top up with diesel to thin it: AdBlue does not mix with diesel, it sinks to the bottom of the tank, where the fuel is drawn from. If you are on a forecourt, whether it is the BP or the Texaco, ask the staff to help roll your car away from the petrol pump. If you're on your own drive around Johnston, leave the car where it sits. Already run? Pull over when it is sensible, then turn off. On the M4, under 50 miles from Johnston, that means the next junction. A short hop across Johnston is a smaller job than a run towards St Davids, under 15 miles away, and so tell us roughly how far it went. ## What happens when our technicians arrive in Johnston Wherever the car came to rest, whether by the local primary school, near The Village Chapel or on your own drive, our van comes to it. We ask what got in, roughly how much, and if it's run, because those answers decide the work and the price. You hear that price by phone, before anyone heads out. Next: draining, then a thorough flush of the whole 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. Once the filter is cleaned — or replaced, if needed — fresh diesel is added, and then your vehicle is tested. Before leaving, we start the car and confirm that it's running smoothly. Unrun cars mostly need a half-hour job from arrival. The equipment is fine on a live forecourt, and hushed enough for a residential street late at night. No money in advance; you settle up on the day. At the end, a VAT invoice and the report from the engineer are handed to you for your insurer. It's worth checking your policy while we travel to you: misfuelling cover is included with many policies. ## About Johnston and where it is Johnston is a village in Pembrokeshire, situated inland at an elevation of 74 metres, and is located near the communities of Pope Hill, Clareston, and Freystrop. Johnston has a population of approximately 1614 people, and its housing stock is predominantly semi-detached. Johnston sits about 14 miles from St Davids, the smallest city in the UK, and is around 209 miles from London. ## AdBlue drains about Johnston, and Pembrokeshire beyond Johnston is a rural village, and our vans that cover it also work the places near it, Clareston and Freystrop among them, across the SA postcode area. Fastest of all: give a SA62 3 postcode to the van. There's no need to move your car. Wherever it sits — beside St Peters Church, in a layby en route to Dawn til Dusk, at home — that is where it gets cleared. Ring and ask instead of guessing if you are near a border, or somewhere hard to explain, like the back of The Johnston Institute. ## In short, for Johnston motorists Before you tip, read the cap. Petrol in Diesel drains it where it stands, anywhere in Pembrokeshire, if AdBlue has gone in the diesel tank regardless — and so leave it off and call 0333 366 0103.