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What is AdBlue and does your diesel car need it?

Many of the latest diesel cars use a fluid called AdBlue in addition to fuel. But what exactly is AdBlue? Here’s everything you need to know.

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By Cazoo editorial team

Many diesel cars that meet Euro 6 emissions standards use a fluid called AdBlue which helps remove toxic substances from the car’s exhaust gases. But what is it? Why does your car need it? Where does it go in the car? Read on to find out.

What is AdBlue?

AdBlue is a liquid added to diesel cars that reduces the harmful emissions they can create. AdBlue is actually a brand name for what’s technically known as diesel exhaust fluid. It’s a solution of distilled water and urea, a substance found in urine and fertilisers. It’s non-toxic, colourless and has a slightly sweet smell. It feels a bit sticky if you get any on your hands but it washes off easily.

Why does a diesel car need AdBlue?

Euro 6 emissions standards apply to all cars built since September 2015. They place very strict limits on the amount of nitrogen oxides, or NOx, that can be emitted legally from a diesel car’s exhaust pipe. These NOx emissions are a waste product of the combustion process – the burning of a mixture of fuel and air inside an engine – that produces the power to drive a car. 

Such emissions have been linked to respiratory conditions that can seriously affect people’s health. Although an individual car emits NOx in very small amounts, add up the emissions from thousands of diesels and the air quality in your town or city can get significantly worse. And that can harm the health of you and your family. AdBlue helps to reduce NOx emissions.

How does AdBlue work?

AdBlue is used as part of a car’s selective catalytic reduction, or SCR, system and is automatically injected into your car’s exhaust system where it mixes with the exhaust gases, including the NOx. The AdBlue reacts with the NOx and breaks it down into harmless oxygen and nitrogen that comes out of the exhaust pipe and disperses into the atmosphere. 

AdBlue doesn’t eliminate all of your car’s NOx emissions, but it does greatly reduce them. 

How much AdBlue will my car use?

There’s no set rate at which cars use AdBlue. In most cases, it takes several thousand miles to empty the car’s AdBlue tank. Some can do at least 10,000 miles before needing a refill. It’s also worth noting that, contrary to some reports, using AdBlue doesn’t mean you’ll burn more fuel.

How do I know how much AdBlue is left in my car?

All cars that use AdBlue have a gauge somewhere in their trip computer showing how much is left. Consult your owner’s manual to find out how to view it. A warning light will show on the driver’s display long before the AdBlue tank becomes empty. 

Can I refill the AdBlue myself?

Not every car allows you to refill the AdBlue tank yourself, but you can easily find out if yours does. Behind the fuel filler flap, there’ll be an extra filler with a blue cap for the AdBlue, next to the regular diesel filler. The tank itself is underneath the car, next to the fuel tank.

AdBlue is available from most fuel stations and car-parts shops. It comes in containers of up to 10 litres, which typically cost around £12.50. The container will come with a nozzle to make pouring the AdBlue into the filler much easier. Alternatively, fuel station HGV lanes have AdBlue pumps that you can use to fill your car if it has a suitable nozzle.

It’s absolutely vital that you don’t accidentally pour AdBlue into your car’s fuel tank. If you do, the tank will need draining and flushing clean. Fortunately, you can’t put diesel in the AdBlue tank because the pump nozzle is far too big.

If your car doesn’t have a dedicated AdBlue filler, the tank can only be refilled by a garage (because the filler is usually hidden below the boot). The tank should be topped up every time your car is serviced, so make sure the garage doing the work includes it. If the tank needs refilling between services, most garages will do so for a small charge.

What happens if my car runs out of AdBlue?

You should never let your car run out of AdBlue. If it does, the engine will go into ‘limp’ mode, which drastically reduces power to keep NOx emissions within legal limits. If that happens, a warning will appear on the driver’s display and you should refill the AdBlue tank as soon as possible. You should avoid turning off the engine until you have access to more AdBlue, because the engine is unlikely to restart.

Incidentally, running out of AdBlue is just one of many reasons that an engine will go into limp mode. Any severe problems with the engine or gearbox that occur while driving will activate limp mode. It’s there to prevent further damage and keep the car moving so you can stop in a safe place to call a breakdown service. 

Which cars use AdBlue?

Many diesel cars that meet Euro 6 emissions standards use AdBlue. By no means all do, though, as there are other systems that can be used instead to reduce NOx emissions.

There are so many cars that use AdBlue that there isn’t the space to list them all here. Still, here some clues to help you figure out whether the car you want to buy uses AdBlue:

  1. Check whether the word ‘blue’ or the letters ‘SCR’ are part of the car’s name. For instance, Peugeot and Citroen diesels that use AdBlue are badged BlueHDi. Fords are badged EcoBlue. Volkswagens are badged TDi SCR.
  2. Open the fuel filler flap to see whether there’s the blue-capped AdBlue filler mentioned earlier. If you’re still unsure, ask the dealer or the manufacturer.

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