What is AdBlue?

If you've bought a diesel car made after 2015, chances are that it may need AdBlue to run. But what is AdBlue, what does it do and why do you need it? This guide explains it all.


What is AdBlue?

Simply put, AdBlue is the trademarked name for a process that reduces the harmful emissions from diesel vehicles.

It’s well-known that diesel engines emit more sooty particles compared to equivalent petrol engines. The most damaging are nitrogen oxides (NOx), which cause smog and acid rain. Nitrogen oxides also contribute to breathing and other respiratory problems among the vulnerable, so it’s no surprise that governments are keen on cutting down emissions from diesel engines. In fact, the British government brought in regulations in 2005 that massively cut down the permissible level of pollutants in exhaust gas.

One popular solution that carmakers have turned to is the use of a Selective Catalytic Reduction (SCR). An SCR injects precise amounts of a ‘Diesel Exhaust Fluid’ (DEF) that neutralizes harmful emissions. AdBlue is just the name under which the DEF is marketed, and it’s a registered trademark of the German Association of the Automotive Industry.

What does AdBlue do?

AdBlue is composed of de-ionised water (67.5%) and urea (32.5%). When the SCR injects AdBlue into the exhaust pipe, the high temperatures cause the release of ammonia, which in turn converts the harmful NOx emissions into two harmless products – water and nitrogen. In case you are wondering, automotive urea is a synthetic product and is not animal-derived.

How can I tell if my vehicle uses AdBlue?

If your diesel car was built after 2016 and the engine complies with Euro 6 regulations, your car will need AdBlue. However, the technology in itself is not new. SCRs have been used in heavy-duty vehicles and some passenger cars since 2004. If your car needs AdBlue, it will likely have a blue or black screw cap for filling up AdBlue next to the black diesel filler cap. Some manufacturers fit the AdBlue cap in the boot or engine compartment.

Popular models that are known to require AdBlue include the BMW X5, Mercedes-Benz S-Class, Volkswagen Passat, Audi Q3 and Citroen Berlingo. There’s often a clue in the car’s model name, such as the use of “Blue” or “SCR”. If you’re unsure, your car manual is the best place to find the answer.

What are Euro 6 regulations and what do they mean for me?

Euro 6 regulations set up by the European Commission in 2014 cut permissible NOx emissions by 56% compared to previous Euro 5 regulations – from 180 mg/km to 80 mg/km. It’s the key reason why more and more diesel car manufacturers have turned to the use of SCR technology. Diesel car buyers should note that Clean Air Zones, such as London’s Ultra Low Emission Zone, require vehicles to be Euro 6 compliant or a daily fee is levied for entry.

How can I tell if my car needs a refill of AdBlue?

Your car will be equipped with AdBlue warning lights or your dashboard will send out reminders to let you know when you need a refill. Your car could refuse to start if you ignore the dashboard warnings for too long. It’s important to note that you need to use AdBlue and failing to do so could invalidate your warranty. On average, you may require an AdBlue refill every 5000 to 8000 miles depending on the manufacturer, model, and driving style.

Can I refill AdBlue myself or do I need to go to a garage?

Garages usually refill AdBlue during routine services. However, you can fill up AdBlue yourself. You may have noticed AdBlue pumps at some petrol stations. AdBlue is also sold in containers that dispense without drips. You can purchase these AdBlue containers online, as well as in most auto stores. A 10-litre bottle of AdBlue should cost around £10.

Is AdBlue harmful?

Automotive urea is generally harmless to humans, although it should be noted that spillage of large quantities can cause an unpleasant stench that can linger in the car for a long time. Please use these precautionary measures to protect your car and yourself:

  • AdBlue can cause damage to paintwork and wiring. Make sure to refill carefully.
  • Do not pump AdBlue into the diesel tank. If AdBlue is pumped into the fuel filler, do not start the engine. Call the emergency support number immediately.
  • Do not pump fuel into the AdBlue tank. If fuel is pumped into the AdBlue filler, do not start the engine. Call the emergency support number immediately.

Can I store AdBlue containers in my car?

High-mileage drivers who will require more frequent refills of AdBlue keep an emergency AdBlue container in the boot. However, urea needs to be stored between -11 and 30 degrees C, and it lasts around 12 months in these conditions. AdBlue will start to decompose above 30 degrees. It’s better to keep emergency containers at home or in the garage rather than in the boot.

Although only a few large diesel cars have started to implement the SCR technology that requires the use of AdBlue, it is likely that more manufacturers will follow suit for all their diesel models. Driving prudently helps reduce the need for AdBlue top-ups, as well as being good for the environment and your pockets.

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