What is AdBlue and how does it work?

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AdBlue - what you need to know

Alongside washer fluid and ice scrapers, we are starting to see containers of AdBlue for sale at garages and even supermarkets but does your car need it? The answer is probably yes, if you drive a modern diesel-engined vehicle. Here’s what you need to know.

What is AdBlue and how does it work?

AdBlue is an additive which is fed into the exhaust system of some newer diesel vehicles. The process is called Selective Catalytic Reduction (SCR). It reacts with the nitrogen oxide (NOx) gas which is produced by the combustion process in the engine and breaks it down into harmless nitrogen and oxygen.

Does my car use AdBlue?

AdBlue use started in commercial vehicles and larger, heavier cars but it is now commonly needed in many family-sized diesel-powered models. If you can’t see an obvious filler cap, you might need to check your car’s manual or with the dealership.

How do I fill up my AdBlue?

If your car uses AdBlue, it will have its own separate tank: it is not simply added to the regular diesel. If you are lucky, an obvious blue or black filler cap will be located next to your fuel filler for easy access. Some are located under the bonnet; others are in the boot and require the removal of the spare wheel to reach the filler.

Some cars need the use of the wheel brace (the tool for removing wheel nuts) from under the boot floor to undo the AdBlue filler cap while others can be opened by hand.

AdBlue can be purchased from dealerships, many filling stations and car accessory shops. There are various sizes, the largest of which require a flexible hose (usually sold with the additive).

Important: You should only use the AdBlue equipment to store or refill AdBlue. The equipment should also be kept clean and free of dirt and dust.

But it's not blue

No, AdBlue isn’t blue; it’s a clear mixture. AdBlue is actually a trade name registered by the German car manufacturers association. There are others but it is the most commonly used exhaust additive.

Will it make my car more expensive to run?

The answer is yes, but not much when compared to the cost of diesel your car will use. Consumption is typically 2-4% of the diesel for cars (although larger vans and lorries may use up to 6%).

In real terms, you’ll pay around an extra £1.50 to £3 for every £100 of diesel spent (assuming £10 for a 10 litre bottle of AdBlue and £1.35 per litre of diesel) to reduce NOx levels in your car’s emissions.

What happens if I don't top it up?

Your car should warn you with a symbol or message when the AbBlue level is low. If you run out, it won’t damage your engine but sensors will detect this. Some cars will prevent you starting the engine once it runs out; others could reduce the engine’s performance, limiting the emissions according to legal standards.

Is it true it's made of urine?

No, this is an urban myth. However, it does contain about a third urea which is a compound also found in urine.

Does it freeze?

Yes AdBlue freezes at around -11degC. However, the water and urea freeze and defrost at the same rate so the concentration should remain the same.

About the Author

Andrew is a freelance motoring journalist with a background in IT and the vehicle leasing industry. With a lifetime’s passion for all things automotive, he can be found behind the wheel of everything from vans to supercars. In addition to reviewing the latest vehicles and technology, Andrew also runs a couple of classic British motors. He lives at the edge of the Peak District with his son and cat.

Andrew Wright @theMotorWriter