What is AdBlue?
If you own a diesel car built after September 2015, the chances are it’ll need AdBlue at some point. Our guide explains all
AdBlue, or diesel exhaust fluid, is still unfamiliar to some motorists but owners of modern diesel cars with engines that are Euro 6 compliant will already know about it. Our guide explains what AdBlue is used for, how it works, where to buy it and what happens if your car runs out of it.
AdBlue is a liquid used to reduce the nitrous oxide emissions of diesel engines and is made up of a mixture of urea and deionized water that is sprayed into the exhaust system. Its widespread introduction coincided with the current Euro 6 emissions standards, which are part of ever more stringent emissions targets that car manufacturers are now required to meet. Without AdBlue, it would be much more difficult to lower the emissions of diesel cars and get them to comply with the latest standards.
AdBlue is normally checked and topped up if needed during a normal service, but you may need to top it up between services. Nearly all cars that require AdBlue are fitted with a gauge that triggers a warning on your dashboard when you're running low.
What is AdBlue used for and why do we need it?
Car manufacturers are governed by various rules, and increasingly these are driven by environmental concerns. The latest emissions regulations, referred to as Euro 6, came into force in 2016 and represented a particular challenge for the development of diesel engines. Much of this required new ways to minimise nitrogen-oxide emissions.
The technology employed is called selective catalytic reduction, or SCR, which involves injecting precise amounts of a liquid into the vehicle exhaust gases to produce a chemical reaction which neutralises harmful emissions.
How does AdBlue work?
To comply with Euro 6 regulations, many new diesel-powered cars built since 2006 use SCR technology to inject tiny quantities of AdBlue into the car’s exhaust gases. When this solution combines with exhaust emissions, it breaks down the harmful mono-nitrogen oxides in diesel exhaust. This technology has been used in buses and heavy lorries for a long time, so its effectiveness has been proven and its reliability is better than ever.
Does AdBlue affect fuel consumption?
Manufacturers have yet to release any data to suggest that Adblue has an adverse effect on fuel consumption. Economy figures for a new diesel car on sale in the UK will factor in any effect from the use of AdBlue in any case.
Developments in engine technology, changes to the way economy figures are calculated and a range of other variables means it’s essentially impossible to find differences in fuel consumption between new and older cars and attribute them solely to the use of AdBlue.
What is AdBlue made of?
AdBlue is a non-toxic liquid that’s colourless in appearance and is essentially a solution of water and urea – a substance found in urine. However, in AdBlue, the urea is exceptionally pure and is of a higher grade than that used in cosmetics, glue or fertilisers. Similarly, the water is demineralised, which is far cleaner than water from the tap.
When buying AdBlue, you should check it meets the correct specification, so look for the ISO 22241 number on the packaging. This may also appear as ISO-22241-1, ISO-22241-2, ISO-22241-3. This will ensure the AdBlue doesn’t damage your car’s SCR catalyst – a costly repair. Assuming your AdBlue meets these specifications, one brand of AdBlue should be pretty much the same as another, in the same way that diesel fuel is fundamentally the same from one retailer to another.
Where to buy AdBlue
Your AdBlue levels should be checked and topped up at every service and your dealer will happily refill it at other times when required but this is rarely the cheapest option. AdBlue is also sold in bottles at fuel stations and you can also order it online.
Can I refill AdBlue myself?
On several mainstream diesel models, the AdBlue filler is located behind the car’s fuel filler cap. It’s usually smaller than the main fuel filler, and will feature a blue cap and markings confirming it should only be used for AdBlue.
If you’re unsure of how to top up your car’s AdBlue, you should refer to the owner’s manual for instructions on how to access the tank - it shouldn’t be difficult. It’s also a good idea to ask the salesman to show you how to refill the AdBlue during the handover of a new car.
Where can I find an AdBlue pump?
Another option for topping up your AdBlue tank is to use an AdBlue pump. These can be found at most big filling stations in the HGV lanes. Some of the pumps feature a specific fuelling nozzle for HGVs and a different one for cars.
An AdBlue pump is usually used by truckers and is often far cheaper and less messy than trying to top-up your tank from a plastic bottle. The filling stations with AdBlue pumps were originally largely restricted to key routes and motorways but more have been added in recent years.
I have an AdBlue warning light? What should I do?
All diesel cars that use AdBlue will give you plenty of warning if you're running low. You’ll usually be alerted with a dashboard warning at around 1,500 miles from running out, along with an amber warning light. This warning will remain on every time you restart your car until the AdBlue levels have been topped up to the desired level.
What happens if you run out of AdBlue?
Ignoring the AdBlue warning light on your dashboard is not advised under any circumstances. If you run out of AdBlue while driving, your car’s performance will likely be affected as it tries to reduce its emissions output by going into ‘limp mode,’ reducing the speed at which you can drive and sometimes turning off your vehicle’s stereo or air conditioning to preserve power.
Once you’ve stopped, the majority of modern cars cannot be restarted while the AdBlue tank is completely empty. Fortunately, this situation is easily avoidable, as AdBlue refills are straightforward and usually relatively cheap if you shop around and do them yourself.
For more information about the current road tax rules, read our in-depth guide.
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