AdBlue: Everything You Need to Know

AdBlue knowledge is highly important for diesel drivers. But do you know what it is and what it does?

If you’re new to the world of diesels, AdBlue might be a foreign concept. You might not realise just how crucial it is.

If you’re in this position, then you’ve come to the right place!

Here at Book My Garage, we love making concepts simpler. After all, you shouldn’t need years of industry experience to understand how your car works! That’s why we’ve created this quickfire guide to AdBlue. It answers everything you need to know in a clear and succinct way.

And it only takes a few minutes to read! So, grab a cuppa and lets get started…


What is AdBlue?

AdBlue is a Diesel Exhaust Fluid, or DEF for short. It is NOT a fuel additive, nor is it an alternative for diesel. There are other DEF options, but AdBlue is the most common.

It is a colourless liquid which is usually found in a small blue tank near your diesel tank.


Adblue tank in diesel car


What is AdBlue made of?

AdBlue contains approximately 2/3 demineralised water and 1/3 concentrated urea. It’s perfectly safe and doesn’t penalise your fuel consumption or reliability, which is handy.

It’s a special mixture, so you’re not putting pure urine into your car. It contains automotive urea which is much more concentrated than human urine. There’s usually about 2-4% urea in pee, so you can’t top it up in a hurry if you’re caught short!


What does AdBlue do & how does it work?

It works alongside your Diesel Particulate Filter (DPF)* and Selective Catalytic Reduction (SCR), to reduce harmful emissions produced by your diesel engine. Your engine carefully injects AdBlue into the exhaust gases to produce less harmful emissions.

How does AdBlue do this?

Well, the ammonia in the urea breaks down the nitrogen oxide emissions to create less harmful exhaust gases. This makes your car much more environmentally friendly and even more fuel efficient!

Most importantly, AdBlue helps you meet strict European emissions standards.

*Not every diesel car fitted with a DPF has an AdBlue tank. However, every car fitted with an AdBlue tank has a DPF.


exhaust fumes
AdBlue helps reduce the harmful impact of these exhaust fumes


Why was it brought in?

In late 2015, Europe introduced their strictest emissions standard yet: Euro 6.

There have been various emissions directives to reduce the environmental impact of diesel engines. The first involved making catalytic converters compulsory in 1992. Over the years, the standards have evolved as we understand more about the impact our driving has on the environment. Euro 6 means that all new cars have to produce even less nitrogen oxide than before. Click here for more information.

That’s where AdBlue comes in.

Coaches, lorries and HGVs first used this technology in the early 2000’s and, since 2015, it’s become standard on every diesel car.


Where is my AdBlue tank?

Usually, it is right next to your fuel tank. Look for a small blue filler cap with the word “AdBlue” written on it.

If it’s not there, check under the car or in the boot. If it’s still not obvious, look in your vehicle’s handbook. It should tell you where to find your tank.

Make sure you also check how easy it is for you to fill your tank up before you run out of AdBlue. Your engine won’t start without it, so you don’t want to run your car dry!


How long does AdBlue last?

1 litre of AdBlue should last you around 600 miles. A standard tank can hold anywhere between 5 and 20 litres of liquid, so low mileage drivers shouldn’t worry about filling up very often.

For drivers covering more than 12,000 miles a year, it’s important to top up your AdBlue tank regularly. You can do that by booking an interim service at one of our 9,000 local garages twice a year! Our service schedule checks you AdBlue as standard (and tops it up when you need it), so you’ll never go without.

Plus, you also get a high-quality interim service from a trusted and recommended garage. Don’t forget to book yours today!


It’s super easy to book a car service online: just follow the link and enter your registration and postcode to start comparing deals!


What is the price of AdBlue?

AdBlue is actually pretty cheap. A 10l bottle costs about £12.50 and a pouring funnel is just a couple of extra quid.

It’s always worth having a small bottle in the car just in case, but there are other places to fill up.


Adblue pump


Where can I buy AdBlue?

You can pick it up in places like Halfords or some supermarkets, like Morrisons and Tesco.

You can also find AdBlue fuelling pumps at motorway service stations up and down the country. HGVs need to fill up regularly and more and more of these pumps are adding car accessibility with more widespread AdBlue usage.

If your AdBlue tank is next to your fuel tank, it’s super easy to fill up at a service station. Just fill up at the pump as you would with diesel.

As always, if you don’t feel comfortable topping your tank up yourself, book an appointment with the professionals.


How do I know when I need to top up?

Your car will let you know. As AdBlue is vital to keep the engine running, there’s a warning light on your dashboard. It usually switches on when you have about 1,500 miles left. That way, you have plenty of time to top up your tank. So don’t delay!


What is the cost of getting it wrong?

AdBlue mistakes can be horrendously expensive. While it’s a fuel additive, it doesn’t mix well with raw diesel, only the exhaust gases. If you accidentally fill up the wrong tank (either diesel in AdBlue or vice versa), don’t touch the ignition! You could cause a small explosion in your engine that’s both dangerous and highly expensive to fix. Stay where you are and immediately call your recovery provider.

It’s also worth noting that not every manufacturer uses the same type of AdBlue. While the basic mixture is the same, there may be some differences across the board. Check what type your car needs before topping up, just like you would with specialist engine oil.



AdBlue is an important fuel additive that reduces engine emissions in diesel cars. It’s fairly cheap to buy and safe to run – but mistakes can be expensive! Always make sure you know the specific details for your car and, if you’re ever in any doubt, book an appointment with a professional mechanic.


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Mandy Weston

Mandy Weston

Mandy is an ex-mechanic, with 22 years’ experience in the motor industry. As an in-house motoring expert, Mandy is the go-to woman for any relevant questions that our customers have; both garages and drivers. From specific problems with your car to general maintenance, Mandy is a reliable source of information and advice. Her passion for motoring is a huge factor to her success and the huge wealth of knowledge that she has. She now uses her remarkable grasp of the industry to write regular content for our readers to help drivers understand their car better, avoid being ripped off by garages and save money on their motoring requirements.

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