What is AdBlue, how much is it and why do diesel cars use it?

A practical guide for drivers

DIESEL cars produced from late 2015 will most likely have an exhaust treatment system that requires AdBlue. This specially formulated liquid is injected into the exhaust system of the car to help neutralise harmful emissions.

In everyday driving the AdBlue system works automatically and goes unnoticed, but it does require refilling over time. If you haven’t had a diesel car before, this guide will help explain everything you need to know about AdBlue. 

What is AdBlue?

One of the latest techniques used to clean up diesel emissions is known as selective catalytic reduction (SCR). A liquid is used to treat exhaust gases and remove harmful pollutants, including nitrogen oxides (NOx), of which nitrogen dioxide (NO2) is the most harmful.

The fluid used in most vehicles is known as AdBlue, a registered trademark owned by the German Association of the Automobile Industry (VDA), which ensures standards are maintained. The fluid is stored in a tank in the car, but unlike petrol or diesel it is not injected into the engine; instead it is fed into part of the vehicle’s exhaust. A chemical reaction converts the harmful NOx exhaust gases into harmless nitrogen and water.

What is AdBlue made of?

Some believe that AdBlue is made from pig urine and is blue in colour, but neither is true. AdBlue is actually a colourless liquid made up of high purity urea and deionized water.

Which cars use AdBlue?

New technology such as SCR and AdBlue is still found mainly in big, expensive diesel models. That is because the system is both too large and too expensive to squeeze into small runabouts.

In tests, small diesel cars without SCR, such as the 2016 Volkswagen Polo 1.4 TDI, have been found to be as toxic as a fully laden lorry. In measurements taken by Leeds University’s Institute of Transport Studies, the Polo emitted 1.2g of NO2 per kilometre travelled, which is the same as a fully laden diesel lorry with a 13-litre engine.

Does my car use AdBlue?

When you buy a new or used diesel car from a dealership, the sales person should explain what features it has and specifically whether it uses AdBlue. Some cars have a blue or black screw cap for AdBlue next to the black diesel filler cap. In others, the cap is in the boot, or in the engine compartment. The vehicle handbook will explain the requirements of your car’s system.

Wherever the filler is, your car will warn you on the dashboard if the AdBlue tank needs a top up (see below).

How long does AdBlue last and how much AdBlue do I need?

The tank that holds the AdBlue solution varies in size between makes and models of car. As a guide, a Volkswagen Tiguan SUV and Passat family car have a 12 and 13-litre AdBlue tank respectively.

The rate at which it is consumed depends on the size of the car and the driving style; the more economical the car and driver, the slower it will be used. VW estimates that the Tiguan and Passat use 1.5 litres of AdBlue every 620 miles, and suggests that a tankful of AdBlue gives a driving range of 3,000-4,000 miles for the Tiguan, and 4,000-6,500 miles for the Passat.

By contrast, Peugeot estimates that its cars can travel 12,000 miles between refills — the same as its servicing intervals.

How will drivers know if AdBlue needs topping up?

The car’s driver information display screen should flash up warnings, much as it would if fuel or windscreen washer fluid were low.

Failing to act on these warnings will ultimately result in the car refusing to start until the AdBlue tank is filled.

Can drivers refill AdBlue themselves?

Garages should refill AdBlue as part of a diesel car’s routine servicing. However, it’s possible to refill a tank of AdBlue yourself.

Some service stations have AdBlue dispensing pumps. Alternatively, garages and filling stations sell portable containers of AdBlue, as do many online retailers, such as Amazon.co.uk and Halfords.com.

Is all AdBlue the same?

Whilst most AdBlue mixes are made up of the same quantities of urea (32.5%) and de-ionised water (67.5%), you may find some solutions called something different, BlueTech or Bluedef, or simply “urea solution”.

Those without the AdBlue trademark may not be of the same quality, and could damage the engine of your car. Therefore, we recommend sticking to branded Adblue, such as the following:

  1. Status AdBlue, 2 x 10L, £18.24 at Amazon – buy here
  2. Halfords AdBlue 3.5L, £6.50 at Halfords – buy here
  3. Redex AdBlue 5L with spout, £10.97 at Amazon – buy here
  4. Greenchem Adblue 10L, £11.99 at Euro Car Parts – buy here

Where to buy AdBlue

As we mentioned above, some service stations will have AdBlue dispensers which you can use to refill your tank. Other places you can buy AdBlue from include:

How much is AdBlue?

The price of AdBlue starts at roughly £5 for a 4.7-litre container, at the time of writing.

Some car makers, including Peugeot, suggest you take the car to a dealer, which will do a refill for a fixed price of £9.99. Vauxhall offers to waive any labour charge if drivers bring their car in for a top-up.

How to reset the AdBlue warning

  1. Fill up your tank with Adblue
  2. Switch on the ignition (not the engine)
  3. Wait for up to one minute, the warning should then clear

If this still doesn’t clear it, we recommend taking the car to your dealership as they can help update the software.

Emergency top-up bottles of AdBlue

Some high-mileage drivers carry 1-litre emergency bottles of AdBlue in the boot of their car, safe in the knowledge that should they need to fill the system at short notice, they will be able to do so. The fluid is corrosive, so some car companies do not recommend this.

AdBlue and your car’s warranty

If your car has a warranty, it is important to use branded AdBlue solution. For any solution to use this trademark, it must comply with certain standards that vehicle manufacturers’ SCR systems rely on. Failing to do so could invalidate the warranty.

What happens if your car runs out of AdBlue?

When your car’s AdBlue level starts to run low it will alert you prior to starting the engine, usually indicating how many miles of driving is remaining. It’s important that you don’t ignore this, as once it runs out it will not be possible to start the engine until the system is refilled. 

If you happen to run out of AdBlue while driving, the engine’s power and performance will be reduced. The car does this to prevent any potential damage to the system occurring. Should this happen it is recommended that you immediately drive to the nearest service station where AdBlue is available and refill the tank. 

Stopping the engine before this will render the car immobile. Once refilled, you may have to wait for the car to reset its system after refilling, but this generally happens automatically. 

Can I use water instead of AdBlue?

Although AdBlue is made up mostly of de-ionised water, you cannot use water to fill the tank. All trademarked AdBlue products meet a specific standard, so it is essential that you avoid using any other product that is not recommended as it could damage your car’s SCR system resulting in costly repairs that won’t be covered by a warranty. 

And water, of course, will do nothing to eliminate harmful emissions from your exhaust.

This article features products that have been chosen independently by Driving.co.uk journalists, and our reviews are unbiased. We may earn revenue if you click the links and buy the products, but we never allow this to affect our opinions.

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