--- title: Explained: AdBlue in a Diesel Tank Cwm-dows canonical: https://www.petrolinadieselcar.co.uk/adblue-in-diesel/cwm-dows-caerphilly/ location: Cwm-dows county: Caerphilly latitude: 51.665330 longitude: -3.154540 service: AdBlue in a Diesel Tank updated: 2026-10-24 --- # Why It Happens and How to Prevent It: AdBlue in a Diesel Tank in Cwm-dows Keep your motor and ignition off then call 0333 366 0103 now — reading can wait if AdBlue is already in the diesel tank. Normally, if the motor hasn't run, it's emptied and fully cleaned where your car is in Cwm-dows. Here in advance? In that case what follows covers how it happens and what to prevent it happening at all. ## Two fillers, two tanks: AdBlue in a diesel vehicle Many newer diesels on the roads round Cwm-dows and Pentwyn-mawr carry two liquids, not one. Diesel goes to the engine. AdBlue goes to the exhaust, where it is sprayed into the gas to fresh it, and it lives in a tank of its own. Each tank has its own filler. On a lot of vehicles the two sit side by side under the same flap; on others the AdBlue filler is in the boot or under the bonnet. The diesel side is fuelled at the petrol pump all the time. Seldom filled, AdBlue usually goes in out of a bottle, tipped by a driver who must stop and think what cap to use. That gap is where the mistake lives. ## How does AdBlue in the diesel tank take place in Cwm-dows? Rarely is it carelessness: usually three things line up. First, the warning. Low AdBlue brings a warning from the vehicle, and running out means limp mode — so a rushed top-up, perhaps before work off Beechwood Close, or outside The Red Lion on the way home after work. The old car's filler is where your hand reaches — but a rental car, a new vehicle or a company car keeps the fillers elsewhere. That's a second factor: an unfamiliar motor. A spouted bottle meets no obstacle at a diesel filler no more than at an AdBlue one. So the pour, after begun, keeps on. Whether it happens in Newbridge or the middle of Cwm-dows, it is the same few seconds. ## Telling the AdBlue filler from your diesel filler Look at these first, on a forecourt around Cwm-dows or a driveway out in Pantside. A few seconds, no more. - Read the cap rather than going by where it sits: AdBlue ones are frequently blue or marked "AdBlue", and diesel caps usually aren't. - On plenty of cars, the size gives it away: AdBlue gets the smaller filler neck. - Look inside the fuel flap: many vehicles have a label there saying which fuel goes where. - Can't see it beside your diesel inlet? Then check beneath the bonnet or inside the boot — the owner's manual will say which. - Check with 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 outside Newbridge. ## How to top up without AdBlue in the diesel tank For the day the warning comes on — anywhere it is across Caerphilly — a routine to use. - Park then switch off. Not on a slope, not with the engine running, and not in a rush on the side of Cwmtorlais Road. - Say "AdBlue" out loud as you unscrew the cap, once you find the AdBlue filler and reading it. Daft, perhaps, yet it works. - If both sit under one flap, check the diesel cap is still closed before you lift the bottle — then leave the vehicle on. - Tip slowly, using the bottle's own spout. Stop when it's full or when the bottle is empty. - Close the cap, and look again — making sure your diesel cap remained shut throughout. Only then, start your car. Discover at the second or third stage that AdBlue went in the wrong tank? That's where you stop. Don't go on to stage five. ## Already put AdBlue in your diesel tank around Cwm-dows? Then the order of things is short. Do not start the motor. The fuel pump starts on many diesels the moment your ignition goes on — and so leave it off. Topping up with diesel will not weaken it: rather than mixing, AdBlue sinks to the bottom of that tank, just where fuel is drawn from. If you are on a forecourt, whether it's the Texaco or the Sainsbury's, ask the staff to help push your car away from the petrol pump. Leave it where it is if you are on your own drive in Cwm-dows. If your motor has already run, stop as soon as it is safe then switch off. Leave the M4 — under 10 miles out of Cwm-dows — at the first junction. About how far did it go? Hopping across Cwm-dows is smaller work than a trip of under 10 miles to Newport, and so say. ## When we turn up in Cwm-dows, what occurs? Our van comes to the car wherever it stopped — your own drive, near Saint Paul's, or outside the local primary school. The replies determine this work and the quote, and so our engineers ask what was put in, about how much, and whether it's run. During the call itself, you are told the price — before dispatch. Your system is then purged thoroughly, after your tank is emptied. With AdBlue that counts 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. The filter flushed or, where needed, swapped; fresh diesel in; then a test of your car. Next we start the car and make sure it runs properly before leaving. With pumps fine on a working forecourt and quiet enough for use outside a house at night, most jobs where your motor hasn't run need roughly half an hour after we are there. You pay on the day, with nothing upfront, and get a VAT invoice and an engineer report for your insurer. Wrong-fuel cover is part of many insurance policies — so make use of the wait to look at yours. ## About Cwm-dows itself Cwm-dows is a suburban area in Caerphilly, situated inland at an elevation of 146 metres, with terraced housing being the predominant type of accommodation. Cwm-dows is located near the cities of Newport and Cardiff, and is close to nearby places such as Newbridge, Ton-y-pistyll, and Old Treowen. Cwm-dows has a population of approximately 2670 residents, and is around 130 miles from London. Cwm-dows sits in a region of south Wales characterised by gently rolling hills and valleys. ## AdBlue drains across Caerphilly, Cwm-dows included Throughout NP postcodes, the teams covering Cwm-dows — a residential suburb — work the surrounding locations too, Old Treowen and Ton-y-pistyll among them. Fastest of all: give a NP11 4 postcode to our van. Shifting the vehicle isn't necessary. Anywhere it stands — beside Newbridge War Memorial, in a layby en route to Windsor Park, at home — that's where it gets emptied. Guessing won't help behind Newbridge Tabernacle Baptist Church, on a border, or anywhere hard to pin down; phone and ask. ## In short, for Cwm-dows drivers Before you tip, read the cap. AdBlue in the diesel tank regardless? Leave the vehicle switched off then call 0333 366 0103; Petrol in Diesel empties it on the spot, throughout Caerphilly.