--- title: Explained: AdBlue in a Diesel Tank Harston canonical: https://www.petrolinadieselcar.co.uk/adblue-in-diesel/harston-cambridgeshire/ location: Harston county: Cambridgeshire latitude: 52.136850 longitude: 0.079960 service: AdBlue in a Diesel Tank updated: 2026-10-24 --- # How It Happens and How to Prevent It: AdBlue in a Diesel Tank in Harston Leave the engine and ignition off then ring 0333 366 0103 first — the rest can wait when AdBlue is already in the diesel tank. In Harston, finding it before your engine turns normally means a drain and a full flush where it stands. Here in advance? Then what follows covers how it happens and how to prevent it happening at all. ## AdBlue in a diesel motor: two tanks, two fillers Diesel goes to the engine — yet plenty of newer diesels driven around Harston and Little Shelford carry another fluid as well. Your exhaust, not the motor, is where AdBlue ends up: dosed into the gas to clean them, from a separate tank. There is a filler for every tank. On a lot of vehicles the two sit side by side under the same flap; on others the AdBlue filler is in your boot or under the bonnet. At the petrol pump, the diesel side gets filled constantly. Someone who has to stop and work out where it goes normally tops up the AdBlue side, from a bottle, and far less often. Mistakes happen in the gap between the two. ## AdBlue in the diesel tank around Harston: how it happens It is rarely carelessness. Three things tend to line up. First, the warning. Low AdBlue brings a warning from the vehicle, and letting it run out means limp mode — so a rushed top-up, perhaps before work off High Street, or outside the pub in the village on the way home that evening. Then your car is new. A hire car, a new vehicle or a company car puts the fillers where your last one did not, and your hand hits for the cap it would have used on the old one. And the bottle fits. A bottle with a spout goes into a diesel filler as easily as an AdBlue one, so nothing stops the pour once it has started. Newton or the heart of Harston: it takes the same few seconds either way. ## The AdBlue filler and the diesel filler: telling them apart Look at these first, at a forecourt in Harston or a driveway out in Foxton. Seconds, that's all. - The cap. The AdBlue cap is often blue, or marked "AdBlue". Your diesel cap usually is not. Read it instead of going by position. - Many vehicles give AdBlue the smaller filler of the two. - Lift the flap and check for a label — many vehicles show which goes in which filler just 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 says which. - Picking up a hire or company car, perhaps at the car park outside Foxton? Ask whoever drove it last before leaving, not once the light comes on. ## Keeping AdBlue out of the diesel tank when you top up A routine for the day the light comes on, wherever across Cambridgeshire that is. - Turn off after you park — level ground, engine off, and not in a rush beside Royston Road on the verge. - Say "AdBlue" out loud as you unscrew the cap, once finding the AdBlue filler and read it. Silly, perhaps, yet it works. - Both behind one flap? Then confirm the lid on the diesel filler is still closed before lifting the bottle. - Tip slowly, using the bottle's own spout. Stop when it's full or when the bottle is empty. - Before starting your car, shut the cap and look again that the diesel cap never opened off. Find at stage two or three that it has already gone into the diesel side? So stop right there. Do not go on to stage five. ## Harston: already put AdBlue in your diesel tank? Brief order, then. First: your motor stays unstarted. The fuel pump runs on many diesels the moment your ignition goes on — so leave it off. Filling up with diesel will not thin it: rather than mixing, AdBlue drops to the bottom of that tank, right where the fuel is taken from. If you're at a forecourt, whether it is the BP or the Esso, ask the staff to help push the car away from the pump. Leave it where it is if you're on your own drive in Harston. If your motor has already run, stop as soon as it is safe then switch off. Harston sits under 3 miles from the M11; there, use the next exit. Distance matters — a quick hop across Harston is a smaller job than heading under 10 miles towards Cambridge — so say about how far it went. ## What takes place when our engineers arrive around Harston Anywhere the vehicle came to rest, be it by Harston and Newton Primary School, beside Harston War Memorial or at home, the van comes to it. Which fluid got in, the amount, and whether it ran: our technicians ask because those replies set both work and quote. You get that quote on the phone, before anyone sets off. The system is then flushed thoroughly, after the tank is emptied. Not like petrol, AdBlue leaves crystals and eats at certain fuel-system metals, and neither washes out by itself. Hence it matters more. After the fuel filter is flushed — or replaced, if required — fresh diesel is added, and finally the car is tested. The motor is started next and tested to be sure it runs correctly, all before our engineers head off. Most jobs are finished in roughly half an hour after our technicians arrive, provided the engine hasn't run — and the pumps we use are fine on a live forecourt yet quiet after dark beside a house. No money upfront; you settle up that day. Afterwards, the VAT invoice and a report from the engineer go to you for your insurer. Plenty of insurance policies include misfuelling cover, so it is worth checking yours while we're on the way. ## About Harston, for a moment Harston is a small village in Cambridgeshire, situated on the River Cam at an elevation of around 17 metres. Harston lies approximately 5 miles southwest of Cambridge, with nearby villages including Newton, Hauxton, and Haslingfield. Harston has a population of around 730 people and is characterised by predominantly detached housing. Harston is located within the Eastern region of England, about 44 miles from London. ## Harston and Cambridgeshire: AdBlue drains across the area Over CB postcodes, our teams that cover Harston — a village — work the surrounding places too, Haslingfield and Hauxton among them. Our van gets to you fastest with a postcode starting CB22 7. No need to shift your car. Wherever it sits — near Harston Village Hall, on a lay-by heading to Harston Rec, on a drive — that's where it gets drained. If you are near a border, or somewhere hard to describe like the back of Harston Village Sign, ring and ask instead of guessing. ## The short version for Harston people Read the cap before you pour. AdBlue in your diesel tank after all? Keep the vehicle off then phone 0333 366 0103; Petrol in Diesel drains it where it stands, across Cambridgeshire.