Emissions standards for modern diesel cars have become significantly tougher in recent years, specifically for the emissions of nitrogen oxides (NOx), so car manufacturers have sought to find ways of reducing NOx levels in diesel car exhausts, and they’ve come up with two main ones. The first is to use an exhaust gas recirculation system to add air from the intake, which helps to reduce the amount of nitrogen that becomes NOx. The second is to use a fluid additive in the vehicle’s exhaust to help reduce the amount of NOx emissions. This additive is known as AdBlue.
Strictly speaking, AdBlue is a trade name, but it’s the most common version of what is strictly called diesel exhaust fluid (or DEF). It’s made from a mixture of urea and de-ionised water. It’s colourless (so, er, not blue at all) and non-toxic.
Since it’s an exhaust fluid, rather than a fuel additive, it’s delivered into your vehicle in part of the exhaust rather than mixed in with the fuel. For this reason, it’s kept in a separate tank, so that it doesn't go through the engine.
What is AdBlue and Does Your Diesel Car Need it?
- Which Cars Need AdBlue?
- How is AdBlue Made?
- How Does AdBlue Work?
- Why Does AdBlue Improve Exhaust Emissions?
- How do I Find AdBlue – Where Can I Buy it?
- How Often do You Need to Refill Your Car's AdBlue Tank?
- What Happens When Your AdBlue Runs Low?
- Where is the AdBlue Tank?
- How do You Refill the AdBlue Tank?
- What Happens if I put AdBlue in the Diesel Tank?
- What Happens if I put Diesel in the AdBlue Tank?
- FAQs
Which Cars Need AdBlue?
Many diesel models built from 2015 onwards (i.e. ones that conform to the Euro 6 emissions standard) require the use of AdBlue. Automotive manufacturers that use AdBlue include Audi, BMW, Citroen, DS, Jaguar, Land Rover, Peugeot, Mercedes-Benz, Renault and Volkswagen.
That’s not an exhaustive list, but you can generally tell whether or not a diesel engine runs AdBlue if the model or trim name has the letters ‘SCR’ or the word ‘blue’ somewhere in it.
If it’s your car or you're physically looking at a car you’re thinking of buying, you can also check the owner’s manual or look for an extra filler cap (generally blue plastic) that will be located next to the fuel filler cap, in the boot or under the bonnet.
If the car uses an exhaust recirculation system, however, it won’t use AdBlue. It’s worth noting, too, that petrol-powered cars don’t use AdBlue at all – only diesel cars use AdBlue.
How is AdBlue Made?
There’s a bit of an urban myth around the production of AdBlue suggesting that it’s made using urea collected from pig urine. While it’s true that there is urea present in the urine of animals, pig urine isn’t pure or sterile enough to make an effective diesel exhaust fluid. Instead, the urea in AdBlue is manufactured rather than sourced from animals.
How Does AdBlue Work?
AdBlue is injected in very small quantities into the hot exhaust system. The heat turns the AdBlue into ammonia and carbon dioxide. The ammonia then reacts with the NOx (the harmful emissions the AdBlue is aiming to eliminate) in a device called a Selective Catalytic Reduction catalyst. This turns the NOx into nitrogen and water.
Why Does AdBlue Improve Exhaust Emissions?
In reducing the NOx content of a diesel car’s exhaust emissions by turning it into water vapour and nitrogen via a chemical reaction, AdBlue helps reduce the emissions of nitrogen dioxides. These pollutants are irritants and can contribute to respiratory issues. NOx can also form smog and acid rain.
How do I Find AdBlue – Where Can I Buy it?
You’ll find AdBlue on fuel station forecourts, motorway service stations, motor accessory shops like Halfords, and general garages. Even some supermarkets stock it. You can also easily source AdBlue from online retailers.
If you’re unsure about exactly what to get, your local dealer will be able to point you in the right direction.
You can get AdBlue in everything from 1.5-litre bottles to 10-litre containers. The smallest bottles have a convenient no-spill neck, so you don’t need a funnel to top up. Thanks to this, it’s a wise idea to keep one of those smaller bottles in the car, so you can top up as soon as your car indicates its AdBlue tank is running low.
How Often do You Need to Refill Your Car's AdBlue Tank?
How much AdBlue you get through will depend on the technical specifications of your car’s engine, your driving style, and how carefully you drive in terms of fuel-efficiency – the more economical your driving, the less AdBlue you’ll use up.
As a rule, you can expect your car to use around a litre of AdBlue every 600 miles, but it could drop to less than 400 miles per litre.
AdBlue tank sizes vary, too, but Peugeot’s guidelines suggest you’ll only need to replenish the tanks in its cars every 12,500 miles, while Audi gives an estimate of around 6,000 miles for an AdBlue-equipped A4 saloon.
Plus, if you have your car serviced or MOT’ed before your AdBlue levels run low, the dealer service department will most likely top it up for you.
What Happens When Your AdBlue Runs Low?
When the levels of AdBlue in your car are beginning to run low, you’ll normally get a dashboard warning light or notice from the car. This is normally when there’s still around three litres of AdBlue left, so you’ll have plenty of opportunity to top it up.
If you do run the AdBlue tank empty, the car’s performance and emissions will deteriorate. The car will also not restart if you switch the engine off while the car has no AdBlue. This is a relatively common cause of breakdowns, and the only way to avoid it is to top up the AdBlue tank without switching off the engine.
What’s more, you can’t switch off or reset the AdBlue warning light manually – it’ll only switch off once you’ve refilled the AdBlue tank. You also won’t be able to simply add a small dash of AdBlue and get going again; it needs to reach a minimum level before the car’s systems will let you drive again.
Where is the AdBlue Tank?
Normally, you’ll find an AdBlue tank in what would otherwise be the spare wheel well (your car will have a temporary puncture repair kit instead of a spare wheel if this is the case).
How do You Refill the AdBlue Tank?
More important than where the tank is located is where to find the filler cap for the AdBlue. In most cars, you’ll find the AdBlue filler cap next to the main diesel filler cap. It’s smaller than the diesel one and generally blue.
If the AdBlue filler cap isn’t hidden behind the main fuel filler flap, then check under the bonnet or in the boot of the car. Check your car's handbook if you still can't find it.
When refilling your AdBlue tank, you should always follow any instructions that are provided on the bottle or container, as well as any found in the vehicle’s handbook.
It can be useful to use a small funnel to ensure you can tip up the bottle or container without any undue spillage. And if you do get any on your hands or the car’s bodywork it’s important to wash your hands or rinse off the affected bodywork thoroughly. This is because AdBlue can damage your car’s paintwork and irritate your eyes and skin – despite the fact that it’s non-toxic.
It’s important to consider storage. You must make sure you keep your AdBlue somewhere no hotter than 30°C and no colder than -11°C. Too cold and it freezes; too warm and it will start to break down and become ineffective. It also has a storage shelf life of around a year.
What Happens if I put AdBlue in the Diesel Tank?
Because of the proximity of the two filling points on most cars, it is possible to accidentally put AdBlue into your car’s diesel tank.
If this happens, there’s a risk of it causing damage to the car’s injection system, fuel pump and fuel tank. This is potentially a very expensive issue and could even mean you’d end up needing a new engine.
It’s therefore vital you don’t start the car if this happens. Instead, call a breakdown recovery service to safely drain the tank and dispose of the contaminated fuel. Only then will you be able to restart the car safely and without risking terminal damage to the engine.
What Happens if I put Diesel in the AdBlue Tank?
It’s a similarly tricky issue as putting AdBlue in your diesel tank. Diesel in your AdBlue system could cause irreparable damage to the AdBlue injection system and the Selective Catalytic Reduction catalyst (SCR system). In a worst-case scenario, the whole system will have to be replaced, which is an expensive fix.
Therefore if you do accidentally put diesel in your AdBlue tank, don’t start the car, and call your breakdown assistance provider for help immediately.
FAQs
How often does AdBlue need to be refilled?
As a general rule, expect your car to use around a litre of AdBlue every 600 miles, but it could drop to less than 400 miles per litre depending on your car and how you drive it. AdBlue tank sizes vary, too. Peugeot says the tanks in its cars will last around 12,500 miles, while Audi gives an estimate of around 6,000 miles for an AdBlue-equipped A4 saloon.
What happens if AdBlue runs out?
If you run the AdBlue tank empty, the car’s performance and emissions will deteriorate, and the car will not restart if you switch the engine off. This is a fairly common cause of breakdowns, and the only way to avoid it is to top up the AdBlue tank without switching off the engine.
Is AdBlue harmful to the environment?
AdBlue is not harmful to the environment. Urea is a naturally occurring substance, and is non-toxic. It is corrosive, however, so spills on skin and surfaces should be quickly diluted with plenty of water and mopped up.