What is AdBlue and what does it do?

ByIsaac BoberSeptember 25, 2019
What is AdBlue and what does it do?

Otherwise known as AdBlue (the marketing name), diesel exhaust fluid which helps to reduce nitrogen oxide emissions is the result of ever-tightening emissions laws in Europe.

Diesel exhaust fluid which is more commonly known as AdBlue arrived with the roll out of Euro6 emissions standards in 2014. And the name? Well, that was a sexy idea by the German Association of the Automotive Industries (VDA) which trademarked the name, AdBlue.

Diesel vehicles offer strong performance, but the downside is that they emit more cancer-causing nitrogen oxide than petrol engines. And, so, knowing the requirements of Euro6 (2014) car makers set about developing a system to reduce nitrogen oxide emissions. AdBlue (diesel exhaust fluid) delivered via a Selective Catalytic Reduction system was the result.

What Is AdBlue?

Used in diesel vehicles, AdBlue (or diesel exhaust fluid) works together with a Selective Catalytic Reduction (SCR) system. As a concoction, AdBlue is nothing more than urea and deionised water; the actual levels are around 32.5% automotive-grade urea (not agricultural grade stuff) and 67.5% deionised water.

AdBlue is stored in a separate tank to your vehicle’s diesel fuel – there’s usually an AdBlue filler cap next to your diesel filler cap (the nozzles for both are different – 19mm for AdBlue and 22mm for diesel). Don’t be tempted to add AdBlue directly into your fuel tank.

Why do we need it?

Car makers are able to build a diesel engine that can burn off almost all of the soot being produced and pumped out the tailpipe via a diesel particulate filter. But the by-product of this excessive amounts of cancer-causing nitrogen oxides being pumped out the tailpipe.

How does it work?

AdBlue is squirted into the exhaust pipe which causes the urea to decompose and convert into ammonia and carbon dioxide (yep, excessive carbon dioxide emissions are also harmful for the environment, but…). Once this hits the SCR the ammonia reduces the nitrogen oxides to nitrogen and water vapour. This process removes around 90% of the nitrogen oxide emissions.

How Long Does A Tank Last?

Most AdBlue tanks will offer, in general driving, up to 10,000km of range before needing to be filled but we’ve heard stories of those who tow only getting around half that range. In general driving, expect to use around 1-2L of AdBlue per 1000km travelled. A tank generally holds less than 20L of fluid.

What happens if I run out?

While your vehicle will continue to run if you run out while driving, it won’t allow a restart once you’ve switched off the ignition.

Does it Freeze?

Yes, and you can’t add anti-freeze agents to it as the sensors are sensitive to anything that isn’t pure diesel exhaust fluid. DEF will remain a liquid up to around -11 degrees C.

Where Do I Buy AdBlue?

You can purchase the stuff in bottles from auto accessories shops and some petrol stations are offering it for passenger vehicles in addition to the truck AdBlue bowsers.

Do I really need AdBlue?

Well, that depends on whether you want your diesel 4X4 belching out cancer-causing nitrogen oxides. This is a product that does a good thing, so, why would you blank off the lines. More than that, the AdBlue will crystallise in the tank if it’s not used and so you’ll need to replace the tank and likely the lines too. So, yes, you, me and the world needs you to leave your AdBlue tank working on your 4×4.