What is AdBlue and does your diesel car need it?

If you own a new diesel, you’re likely to have to keep it topped up with a special liquid that eliminates NOx emissions...

What is AdBlue and does your diesel car need it?

The permissible level of pollutants that new cars can emit has been reduced significantly in the past couple of years. The introduction of the latest Euro 6 standards demanded a 67% drop in nitrogen oxides (NOx) in the exhaust emissions of diesel cars.

Car makers have found two ways of meeting these standards: selective catalytic reduction and exhaust gas recirculation.

The first measure uses an exhaust fluid, commonly AdBlue, to break NOx in exhaust gases down into harmless elements before it’s expelled from the car.

The second uses a recirculation system to replace some of the exhaust gas with intake air to reduce the amount of nitrogen that can be turned into NOx. Owners of cars fitted with this type of system don’t need to use AdBlue.

What is AdBlue and does your diesel car need it?

What is AdBlue and what does it do?

AdBlue is the trade name for a type of diesel exhaust fluid. It's a mixture of urea and deionised water that’s stored in a separate tank from the car’s fuel.

When the car’s engine is running, tiny amounts of AdBlue are squirted onto the exhaust gas produced, turning the NOx into nitrogen and water.

Which cars need AdBlue?

Many diesel cars registered after September 2015 use AdBlue to reduce emissions. In general, if you own a Euro 6-compliant diesel Audi, BMW, Citroën, Jaguar, Land Rover, Mercedes-Benz or Peugeot, it’s likely to use AdBlue technology. There’s often a clue in the car’s model name, which may have 'Blue' or 'SCR' in it.


What is AdBlue and does your diesel car need it?

How often does AdBlue need topping up?

The amount of AdBlue used depends on the type of driving being done and the number of miles covered.

Audi says its A4 saloon has a 12-litre AdBlue tank that gives it a range of approximately 6000 miles between top-ups. Peugeot says the AdBlue tanks in its cars should only need topping up every 12,500 miles and, if you don’t cover that many miles a year, the fluid will be topped up for you during the car’s annual service.

How do I top up my car’s AdBlue?

Most AdBlue tank filler spouts are situated next to the diesel filler, and they usually have a blue cap. Other common places for fillers include the boot and spare wheel well. The owner’s handbook should tell you its location.

What is AdBlue and does your diesel car need it?

Where can I buy AdBlue and how much does it cost?

Car accessory shops and fuel stations sell 10-litre and 20-litre containers of AdBlue. You can also buy it online, while some petrol stations sell it at the pumps, too. Expect to pay around £1.50 per litre if you’re buying it in a container or about 60p per litre from a service station pump.

What happens if my car runs out of AdBlue?

Most cars will display a dashboard warning light when the AdBlue is starting to run low; this usually illuminates when there’s around three litres of fluid left, giving you approximately 1200 miles to refill it.

If you ignore the warning and carry on driving the car until the AdBlue runs out, the car's emissions and performance will be adversely affected. Once you’ve turned the engine off, the car won’t restart if the AdBlue has run out.

The AA estimates that it dealt with around 20,000 AdBlue-related breakdowns in 2017. So if you’ve run out and are still driving, stop the car to top it up but don’t turn the engine off.

What should I do if I put diesel in the AdBlue tank?

Don't start the engine; call your dealer or breakdown service provider to get the tank drained. If you start the engine, you could damage the selective catalytic reduction and AdBlue injection systems and they may then have to be replaced.

What should I do if I put AdBlue in the diesel tank?

It’s important not to start the engine or you risk writing off the engine and fuel system. Call a breakdown company or misfuelling service provider and get the car’s fuel tank emptied and flushed out.

Should you be running a diesel car, or would a petrol, hybrid or electric car suit you better? Our free What Fuel? tool can help you decide with four easy questions.


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