--- title: AdBlue in a Diesel Tank Treforest? Read This canonical: https://www.petrolinadieselcar.co.uk/adblue-in-diesel/treforest-rhondda-cynon-taf/ location: Treforest county: Rhondda Cynon Taf latitude: 51.587170 longitude: -3.326870 service: AdBlue in a Diesel Tank updated: 2026-10-24 --- # Why It Happens and How to Avoid It: AdBlue in a Diesel Tank in Treforest If AdBlue is already in your diesel tank, stop reading for a moment: leave your engine and your ignition off and phone 0333 366 0103. A drain and a thorough flush, done just where the vehicle sits around Treforest, is usually what it takes if found before your engine runs. Here in advance? Then the rest explains how it happens and what to stop it happening at all. ## AdBlue in a diesel motor: two tanks, two fillers Many newer diesels on the roads round Treforest and Graig carry two liquids, not one. Diesel goes to the engine. AdBlue's own tank keeps it, and from there it goes to your exhaust, and there spraying cleans the fumes. Different tanks, separate fillers. Under one flap, side by side: that is the layout on many vehicles. On others, AdBlue's filler sits under the bonnet or in the boot instead. The diesel side is fuelled at the petrol pump all the time. Far less regularly, the AdBlue side gets topped up — normally from a bottle, by someone thinking about where it goes. That gap is where the mistake lives. ## How does AdBlue in your diesel tank occur around Treforest? Carelessness rarely explains it. What does is three things lining up at once. The warning comes first. As AdBlue runs low your car tells you, and if it runs out altogether, the car goes into limp mode. So the top-up is done in a hurry: on a driveway off Forest Grove before work, or in the car park at Otley Brewpub & Kitchen on the way home. New-to-you motors are second, too. Rentals, new vehicles and company motors put their fillers in new places, and habit goes for the cap used on the old one. Nothing halts the pour after it has started, since a bottle with a spout goes into a diesel filler as easily as an AdBlue one. The bottle fits. Whether it occurs in Glyntaff or the middle of Treforest, it's the same few seconds. ## Which filler is for AdBlue, and which for diesel? Be it a Treforest forecourt or a driveway out in Pen-y-rhiw, spend a few seconds over these before anything goes in. - Blue and lettering: an AdBlue cap is regularly blue, or says "AdBlue", where a diesel cap normally doesn't. Trust the cap, not where it sits. - On many motors, the size gives it away: AdBlue gets the smaller filler neck. - A label inside the fuel flap frequently says which fuel goes where, on many vehicles. Look for it. - The handbook. If your filler is not by your diesel cap, it's in your boot or under the bonnet, and the handbook says which. - Collecting a hire or company car, perhaps at the car park outside Trefforest? Ask the person who drove the car last before leaving, rather than once the light comes on. ## Topping up AdBlue without it reaching your diesel tank For the day the light appears — wherever you are in Rhondda Cynon Taf — a simple routine to use. - Not in a rush on the side of Llantwit Road, not on a slope, not with your motor running: park and switch off first. - 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 your diesel cap is still closed before you lift the bottle. - Tip slowly, using the bottle's own spout. Stop when it is full or when the bottle is empty. - Close the cap, and look again — making sure your diesel cap remained shut the whole time. After that, start your car. Find during the second or third stage that the bottle went in the wrong filler? That is where you stop. Skip stage five entirely. ## Put AdBlue in the diesel tank around Treforest already? Brief list, then. Top of it: your motor stays unstarted. The fuel pump runs on plenty of diesels the moment your ignition is switched on — and so keep it off. Thinning it with extra diesel fails, since AdBlue sinks to the bottom rather than mixing — and that is where your fuel is drawn from. On a forecourt — Sainsbury's, Asda or another — the attendants will usually help push the car clear, if you ask. Leave it where it is if you are on your own driveway in Treforest. Already run? Stop when it's sensible, then switch off. On the M4, under 10 miles from Treforest, that means the next exit. Roughly how far did it go? Hopping across Treforest is smaller work than a run of under 10 miles towards Cardiff, so tell us. ## Our arrival around Treforest, and what occurs next Wherever the car has stopped, be it by the local primary school, beside University of South Wales Art Collection Museum or on your own drive, our van travels to it. Both the work and our price depend on three replies — which fluid, what quantity, and if it has run — so our engineers ask. That quote is given on the call, ahead of any van leaving. Then the tank is cleared and the fuel system rinsed thoroughly. Not like petrol, AdBlue leaves crystals and eats at some fuel-system metals, and neither clears away by itself. That is why it matters more. A test is last: before that, fresh diesel goes in, and the fuel filter is flushed or replaced as needed. We do not go until it has been started and is running properly. If your engine has not run, the majority of jobs take about half an hour once we are there, using pumps that are safe on a busy forecourt and quiet enough to use outside a house after dark. No money in advance; you settle up on the day. Afterwards, a VAT invoice and the report from the engineer go to you for the insurer. Wrong-fuel cover is included in many insurance policies — and so make use of the wait to look at yours. ## About Treforest Treforest is a suburban area in Rhondda Cynon Taf, situated on the banks of the River Taff at an elevation of 83 metres. Treforest lies approximately 9.8 miles north of Cardiff and is surrounded by nearby communities such as Glyntaff and Rhydyfelin. Treforest has a mix of housing types, with terraced housing being predominant in the area. Treforest is connected to the wider region by its proximity to major roads and the river corridor. ## Treforest and Rhondda Cynon Taf: AdBlue drains across the area As a residential suburb, Treforest has the same vans as surrounding places — Rhydyfelin, Pen-y-coedcae — all the way across CF postcodes and the wider area beyond. Fastest of all: quote a CF37 1 postcode for the van. No need to shift the car. Draining happens on the spot, be it a drive, a road near Sports Hall, or a lay-by on the way to Coed Craig-lwyd. Assuming doesn't help behind Castle Square United Reformed Church, on a boundary, or somewhere hard to pin down; phone and check. ## In short, for Treforest people Read the cap before you pour. Even so AdBlue in your diesel tank? Petrol in Diesel can drain it where it is, wherever around Rhondda Cynon Taf: keep the car off and call 0333 366 0103.