As emissions controls became stricter in Europe, car makers with diesel vehicles needed a way of cleaning up nitrogen oxide emissions. Diesel Exhaust Fluid (AdBlue) was born.

Updated July 26 2021

AdBlue (the marketing name for diesel exhaust fluid) arrived (for diesel vehicles) with the introduction of Euro6 emissions standards in 2014. Australia is hovering around Euro5 standards. That said, most new cars sold in Australia that are also sold in Europe are Euro6 compliant.

Diesel vehicles offer strong performance and mileage but the downside is they release more cancer-causing nitrogen oxide than petrol engines. With the introduction of Euro6 car makers had to develop a system to reduce harmful nitrogen oxide emissions and AdBlue (diesel exhaust fluid) delivered via a Selective Catalytic Reduction system was developed.

So, what is AdBlue?

Used in diesel vehicles, AdBlue (which is a diesel exhaust fluid) works hand in hand 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). You should never add AdBue directly into your fuel tank.

How does AdBlue work?

Car makers know how to build a diesel engine that can burn off all the soot produced but the by-product of this is excessive nitrogen oxide emissions and that stuff can cause cancer as can the fine soot being shot out of the tailpipe and into the atmosphere (diesel particulate filters were developed to deal with that). So, while diesel engines have their many benefits they also have some horrific negatives.

To deal with the nitrogen oxide emissions, 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…) – the water evaporates. 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.

What’s in a name?

For those who like pub trivia, AdBlue is a name trademarked by the German Association of the Automotive Industry (VDA) because it sounds way sexier than diesel exhaust fluid. But, no matter what the stuff is called by different car makers and producers, it’s all just diesel exhaust fluid.

How long does a tank of AdBlue last?

That depends on the driving you do, but the general rule of thumb is around 1-2L of AdBlue per 1000km travelled. Most AdBlue tanks hold less than 20L of fluid. Most vehicles running AdBlue will warn you when you’ve got around 2000km of fluid left.

Do you really need to refill the AdBlue tank?

Yes, yes, you do. 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. And you can’t trick the thing either. The sensors are clever enough to know when any fluid other than AdBlue has been stuck into the tank and so won’t let you restart the vehicle.

Do diesels run AdBlue and DPF?

Yes. They’re all part of the anti-pollution system. They’re not connected and one will still work if the other one doesn’t but unlike a blocked DPF (where the vehicle will still start) that will need to be manually cleared by a mechanic, an empty AdBlue tank will mean your vehicle won’t start until the tank is filled again.

Does AdBlue 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. But unless you’ve got winter diesel and/or anti-waxing agents in the diesel you’ll have more issues than just frozen DEF.

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.