What is AdBlue and what does it do?

What is AdBlue?

AdBlue is a chemical – made from purified and demineralised water and urea – that helps reduce the harmful emissions produced by diesel engines. If you drive a petrol-powered car, you won’t need to worry about it.
Car manufacturers use AdBlue to keep on top of ever tightening emissions targets. The current regulations in place are the Euro 6, with Euro 7 anticipated to roll out from 2026 onwards.

What does AdBlue do?

Most diesel cars built since 2016 use a technology called selective catalytic reduction (SCR), which basically injects tiny amounts of AdBlue into the car’s exhaust gases. When this happens, and the AdBlue meets the hot exhaust, it releases ammonia, and leads to a chemical reaction which breaks down the harmful bits (nitrogen oxide and nitrogen dioxide), and produces harmless nitrogen and oxygen.

Does my car use AdBlue?

You might not be aware if your car needs AdBlue until the warning light comes on the dashboard, but it’s a good job to check if your car is fitted with SCR technology before then.
Speak to the dealer or manufacturer you’ve bought your car from, or have a look in the handbook. The AdBlue filler cap is usually beside the fuel cap, but it can be in the boot, or sometimes under the bonnet too.

How do I refill AdBlue?

If you cover a lot of miles and have a new-ish diesel car, you might have to top up your AdBlue between services. But it’s easy to do. Open the AdBlue filler cap, open your bottle of AdBlue, and let it pour into the tank. Most AdBlue comes in a handy container that won’t drip.
Avoid getting it on your paintwork as it could damage it. Although it’s pretty harmless to people, it’s best to use gloves and wash your hands if you get any on you.

How to reset AdBlue warning?

You might have to add a minimum amount when refilling the AdBlue to get the warning light off your dashboard - typically three to five litres.

What is AdBlue made of?

All AdBlues are made from 32.5% urea and 67.5% deionised water. This is why its official name is AUS32 which stands for Aqueous Urea Solution 32.5%.

Where to buy AdBlue?

You can buy AdBlue from fuel stations, supermarkets, Halfords, Amazon and service stations. On Amazon, for example, the best seller 10-litres of AdBlue costs £10.

Does AdBlue go off?

If you keep a half-empty bottle of AdBlue in your garage, the particles in the air will contaminate it and can change the chemical composition, so it’s best to use it within its shelf life. Usually, an unopened bottle is okay to use within 12 months while an opened bottle is okay to use within six months.

Is AdBlue flammable?

No, AdBlue is a non-toxic and non-flammable solution, but it should be stored in cool, well-ventilated place and kept away from sunlight to prevent it from degrading.

How much AdBlue does my car need?

Annoyingly, there’s not a magic formula to know how much and how quickly your car will use AdBlue. It depends on what car you own, your mileage, how you drive, and environmental conditions. AdBlue tank sizes also vary from model to model (typically between five and 20 litres), although most manufacturers do calculate how long an average tank of AdBlue will last.
If you have fixed-price servicing, topping up AdBlue will most likely be included in this cost. But if you pay for your services individually, it may well be cheaper to top it up yourself.

What happens if my car runs out of AdBlue?

If your car runs out of AdBlue completely, it won’t start. But you do get plenty of warning before that happens.
Now that you know how AdBlue works, browse for diesel cars on Autotrader.