Most people have heard of AdBlue, but unless you run a Euro-6 compliant diesel engine, you're probably not sure what it is. So in this article, we are going to look at what AdBlue is, why you need it, how it works and what type of engines require it.

What is AdBlue?

AdBlue is a brand name owned by the VDA (Association of German Vehicle Manufacturers). The proper name for AdBlue is diesel exhaust fluid. The VDA licenses the manufacturing of AdBlue to various chemical companies around the world.

Other brands make AdBlue alternatives, including BlueTec and Bluedef. However, most people just refer to these as AdBlue, even if it is not made or distributed by an official AdBlue distributor.

So what is AdBlue? It’s a chemical that, when sprayed into the exhaust system of diesel engines after combustion, can help to reduce harmful nitrous oxide emissions. AdBlue was introduced as part of the Euro-6 emissions standard which came into effect in 2016.

How does it work?

AdBlue forms part of a Euro-6 standard diesel engine's Selective Catalytic Reduction (SCR) system. The chemical is automatically injected into the exhaust after the exhaust gases have passed through a diesel particulate filter.

Once injected, AdBlue reacts with the nitrous oxide (NOx) contained in the exhaust gases, breaking it down into oxygen and nitrogen. These harmless gases then pass out of the exhaust pipe where they are dispersed into the atmosphere.

AdBlue doesn't remove all of the toxic NOx emissions, but it can reduce emissions by up to 90%. Along with NOx reduction, AdBlue also helps to reduce carbon monoxide emissions by 50-90% and particulate emissions by 30-50%.

One further benefit of using AdBlue is that it can reduce total fuel consumption by between 2-6%. According to test data from the AA in the United Kingdom, one litre of AdBlue can increase the range by as much as 500-1000 km.

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Where can you buy AdBlue?

AdBlue is available from most petrol station forecourts in Australia. You can buy it straight from the pump in the same way you buy diesel fuel. Some cars have a separate AdBlue filler cap located next to the diesel fuel filler for convenience.

You can also buy AdBlue at most car accessory stores or petrol station forecourts. This is available in 5 to 20-litre containers which is a great size to keep in the boot as a top-up when you need it. However, buying AdBlue in containers is more expensive than at the pump.

What is AdBlue made from?

AdBlue is made from a combination of 32.5% high-purity urea and 67.5% distilled water. Urea, also known as carbamide, is an inorganic compound produced as a by-product by most mammals. However the urea used in AdBlue is synthetically produced.

Most AdBlue sold in Australia is produced to the ISO 22241 international standard. This helps to protect your engine and exhaust system from contamination. Using a low-quality alternative to AdBlue may result in costly repairs to your vehicle's SCR system.

Can you use water instead of AdBlue?

Because AdBlue is made up of mostly distilled water, this has led to the misconception that AdBlue can be replaced with tap water to achieve the same effect. But this is categorically NOT true.

The active ingredient in AdBlue is urea which contains ammonia. This is what reacts with NOx to neutralise emissions. Replacing AdBlue with distilled water will have no impact on emissions whatsoever and may damage your engine.

Tap water contains many minerals and ions that will damage your vehicle's Selective Catalytic Reduction system. These systems are incredibly expensive to replace, so don’t add tap or distilled/deionized water to your AdBlue tank.

You should also avoid diluting the AdBlue mix with distilled water in an attempt to save money. This will reduce the impact of AdBlue and increase your NOx emissions. You will also eliminate any promised fuel efficiency gains, so doing this is a false economy.

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Do all diesel cars need AdBlue?

AdBlue is only necessary on newer diesel vehicles fitted with an SCR system. These are engines that meet the Euro-6 standard. In practice, that means any diesel car sold in Australia after 2016.

If in doubt, consult your vehicle handbook. This will tell you if AdBlue is necessary and show you where the AdBlue tank and filler nozzle are located. You should also look in the handbook for any special filling instructions your vehicle has.

Is AdBlue a fuel additive?

AdBlue is NOT a fuel additive. While it does combine with the exhaust gases, this must be done after combustion has taken place. Adding AdBlue directly to the diesel tank risks damaging the fuel tank, fuel filter and injection system.

If you have added AdBlue to the fuel tank by mistake, DO NOT start the engine. Call your local breakdown repair service and arrange to have your fuel tank drained.

How much does AdBlue cost?

According to AUSBlue, the largest supplier of licensed AdBlue in Australia, the retail price ranges from $1.50 to $2.50 per litre. The actual cost will depend on the quantity purchased and whether you buy it straight from the pump or in a bottle.

The price of AdBlue does rise and fall in line with demand, but AdBlue is not under the same price pressures as diesel or petrol, so prices tend to stay stable across the year. AdBlue is also not subject to fuel excise tax, which helps to keep costs down.

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How long does AdBlue last?

The rate at which your AdBlue needs topping up will depend on your driving style, engine size and the capacity of the AdBlue tank. But as a rough estimate, 1 litre of AdBlue is used every 500 to 1000 km.

Most modern diesel cars have a 5-20 litre AdBlue tank, so the tank will need topping up every 2,500 to 20,000 km. If you do less mileage than this, your dealer will top up your AdBlue for you and you won’t have to do anything.

If you do higher mileage than this, you will need to top-up levels periodically. Most cars have an AdBlue indicator on the dashboard to warn you when a top-up is required. That’s why it is a good idea to keep a small bottle of AdBlue with you at all times.

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Jordan Ballard

Jordan Ballard

Automotive Content Editor

Jordan is a car finance and automotive industry specialist at Only Cars. With over 20 years of experience with frontline and management roles in sales, finance and other areas, Jordan has an incredible understanding of the automotive industry. As Automotive Content Editor, Jordan loves sharing his passion for cars with the Only Cars audience.