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All about AdBlue

If you drive a diesel car registered since 2014, you might see a warning light indicating that an AdBlue top-up is required. But what exactly is AdBlue?

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If you drive a diesel-engined car registered since 2014, chances are you might one day encounter a warning light indicating that an AdBlue top-up is required.

Don’t worry though, as The Car Expert has put together this handy guide to everything you need to know about what AdBlue is and what you need to do.

The good news is that it keeps your engine environmentally friendly, is relatively inexpensive and you can top-up yourself. The bad news though is if you ignore the warning light for too long your engine will fail to start.

The AA reported the number of AdBlue-related breakdowns went up every month over the course of 2016 with the organisation now dealing with more than a 1,000 every month, those figures are set to grow as more cars hit the road.

Why was AdBlue introduced?

When the latest Euro-6 engines became mandatory from 1 September 2014, the EU ruled that new diesel engines needed to reduce harmful NOx (nitrogen oxides) pollutants emitted by diesel engines by 56% over the previous generation Euro-5 engines.

It was a tall order, but the car industry responded with an additive, trademarked AdBlue, which helps break down NOx in the exhaust system.

The technology has been around in heavy good vehicles since around 2004 and is now pretty much standard in diesel car and van engines bigger than 1.6 litres.

What is AdBlue?

AdBlue is a diesel exhaust fluid (DEF) consisting of synthetically produced urea (reports of AdBlue using animal urine are an urban myth) mixed with deionised water. It’s non-toxic, non-flammable and biodegradable.

AdBlue can be purchased in bottles from service stations, car accessory shops and online.

Expect to pay around £1.50 for a 1-litre bottle and £10 for a 10-litre container. However, the smaller bottles are designed to screw directly on to the filler and are therefore easier to dispense.

Also, look out for blue pumps springing up next to diesel pumps at service stations around the country with prices from around 60p a litre.

How much you’ll need depends on your tank size, which is separate from your fuel tank, and can vary from 5-20 litres.

Usage depends on driving style so to be on the safe side reckon on one litre per 500-600 miles, so if you’re a high-mileage company car driver you’ll need to make regular top-ups.

How does it work?

Here’s the clever scientific part. The technology behind AdBlue is called Selective Catalytic Reduction (SCR), which requires the controlled injection of AdBlue into the exhaust chamber, when the engine’s running.

The aqueous urea vaporises and decomposes to form ammonia and carbon dioxide. Within the SCR catalyst, the NOx are catalytically reduced by the ammonia into water and nitrogen, which are both harmless; and these are then released through the exhaust.

The process neutralises NOx emissions by 80-90%. It can also help reduce fuel consumption by up to 5%.

AdBlue filling point at a BP petrol station.

How do I know when to top-up?

All cars equipped with SCR technology will have warning lights as standard and these will typically alert you when you’re down to around three litres or 1,200 miles, depending on your driving style.

SCR-fitted cars also have an on-board computer display with a read-out of the current level.  Some will also tell you how many starts you have left when the level is low, if you exceed it your car will not re-start as it would be operating with illegal emission levels. A trip to your dealer would then probably be required to reset the system.

Depending on annual mileage and usage you may not need to do your own refills as they could fall within the car’s scheduled annual services, so your dealer will do it for you; although there will be a charge.

How do I know if my car requires AdBlue?

If it’s diesel-engined and was registered after 1 September 2014 then chances are it requires AdBlue.

Also, some brands have helpfully incorporated the word Blue into model names: Mercedes-Benz Bluetec, Peugeot and Citroën BlueHDI and Ford EcoBlue.

Where’s my AdBlue refilling point?

Unfortunately, carmakers have not standardised on the location for the refilling point which explains why some owners are oblivious that their car requires AdBlue until the warning light comes on.

The most obvious and owner-friendly place is behind the fuel flap alongside where you fill up with diesel, with the AdBlue point bearing a distinctive blue cap.

However, many brands have opted to locate it in under the boot floor, with some even positioning inaccessibly under the spare wheel, making refills a chore.

If in doubt check your owner’s manual.

Can I put AdBlue straight into the diesel tank?

Absolutely not! Putting AdBlue direct into your diesel tank can cause you a world of misery akin to misfuelling with petrol.

If you do this then don’t switch on the engine. Immediately contact a reputable specialist to drain your tank.

Likewise, if the filling point is in the engine bay, as it is on many vans, you don’t want to get it muddled up with screenwash or oil.

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Curtis Hutchinson
Curtis Hutchinson
Curtis Hutchinson is a member of the Guild of Motoring Writers and has been a senior motoring journalist for over 25 years. He has written extensively about the automotive industry as editor of both Company Car and Motor Trader where he won the coveted Newspress Business Publication of the Year Award. His work also appears in Fleet World and Fleet World International. In 2016 he was part of the founding team behind the relaunched London Motor Show.