AdBlue, also known as Diesel Exhaust Fluid (DEF), is an important liquid that is used to reduce the emissions from diesel engines. It helps diesel cars, trucks, buses and other vehicles to comply with the strict modern emissions regulations for nitrogen oxides or NOx.

What is AdBlue Made From?

AdBlue is an aqueous urea solution made up of 67.5% deionized water and 32.5% high purity urea. The urea breaks down in the exhaust system into ammonia, which reacts with the nitrogen oxides emitted by the engine. This chemical reaction turns the harmful NOx gases into harmless nitrogen and water vapor.

Why Was AdBlue Introduced?

AdBlue was introduced in the mid-2000s as diesel engines had to become cleaner and comply with stricter emissions standards, particularly in Europe. These standards, known as Euro 4, Euro 5 and Euro 6 progressively reduced the permitted levels of particulate matter and NOx that diesel vehicles can emit.

Without AdBlue, diesel engines would struggle to meet the latest Euro 6 emissions regulations. AdBlue provided an effective method to reduce NOx from the exhaust system. Modern diesel cars with AdBlue can be as clean as equivalent petrol models.

When Should I Refill the AdBlue Tank?

Most vehicles have an AdBlue gauge on the dashboard to show you the fluid level. Unlike fuel, AdBlue is consumed in small amounts - around 2-3% of diesel consumption. In a typical diesel car, an AdBlue refill may be needed every 10,000 - 20,000 km or longer.

If the tank runs dry, the car will prevent you from restarting the engine once stopped. So, when the warnings lights indicate, you must refill AdBlue before it runs out completely. Most gas stations now have AdBlue pumps for easy refilling.

What Happens If I Don’t Fill Up AdBlue?

Modern diesel cars have an emissions control system that relies on AdBlue. Without it, the pollutants would exceed limits by up to 10 times. As a result, manufacturers have made it essential for compliance with emissions regulations.

If AdBlue runs out, emergency warnings will trigger telling you to top up. If ignored, the car will initially enforce speed limits. After that, engine power limits will kick in. Soon the engine will not restart at all once turned off.

Some car makers have additional sanctions. BMW for example cuts audio, climate controls, seat cooling and other driver comforts when AdBlue is below the minimum level. Filling AdBlue is therefore essential to retain functionality of a modern diesel car.

What Causes AdBlue Problems and Is It Bad for My Engine?

Providing you refill AdBlue on time when the car prompts you to, it shouldn’t cause issues. If the product meets specification (as per ISO 22241) and you avoid spillage, it won’t harm your diesel engine or exhaust system. Please follow the car maker's guidelines for which AdBlue to use.

However, problems that can arise with AdBlue system include:

•      Contamination issues if water gets into the AdBlue tank during topping up. Impurities like copper can also impair the emissions control system.

•      Excessive buildup of deposits from spilled AdBlue that have not been cleaned properly.

•      The fluid can freeze in very cold winter climates below -11° C. So, garaging the vehicle or using anti-freeze is recommended.

•      Errors may be displayed if the quality of AdBlue does not comply with ISO 22241. Unapproved sources can cause diagnostic trouble codes.

•      Leaks, blocked pipes, failed sensors or failed reactions in the catalyst. The AdBlue alert system will show errors.

Overall, though, AdBlue gives reliable service provided the tank is refilled promptly when the vehicle notifies you to do so. And you avoid spills or water ingress when topping up.

Using high quality AdBlue from approved suppliers will ensure optimum performance. And no damage to critical emissions control components under the vehicle body.

How Much Does AdBlue Cost to Refill?

AdBlue works out significantly less expensive than fuel over equivalent distances. In most countries, a liter of AdBlue costs around half of diesel per liter. With consumption approximately 3% of the diesel used, the cost is far less.

Based on average fuel economy and today’s prices, you would pay around 2 to 6 cents per mile on AdBlue. Compared to 10 to 30 cents per mile for diesel fuel. Over a year of driving AdBlue works out under $100, versus $1000+ for diesel.

So AdBlue is not a major part of servicing costs. Especially considering the environmental benefits that clean diesel engines can bring compared to older technologies.

AdBlue in Cold Climates

In very cold climates, it's crucial to garage vehicles to prevent solidification in the AdBlue tank. Nighttime outdoor temperatures persisting below -11°C may cause the urea solution to crystalize. This can interrupt the supply pipes and SCR system.

Use of anti-freeze is recommended by some manufacturers if ambient temperatures regularly drop under -15°C. This lowers the freezing point a few more degrees below the nominal -11°C. The anti-freeze needs topping up at recommended intervals, usually annually.

Driving the vehicle regularly prevents freezing up. If crystals do form, they will re-liquefy upon warming. So, heating the tank and lines by running the engine up to operating temperature will restore proper flow. But keeping AdBlue from freezing in the first place is ideal to avoid interruptions in the emissions control system.

The Future for AdBlue

AdBlue has been crucial for diesel engines to reduce emissions and comply with strict limits on nitrogen oxides. As standards tighten even further (for example with Euro 7 in Europe) AdBlue and SCR systems will continue playing an important role well into the next decade.

Even though electric vehicle adoption is accelerating, diesels remain an affordable option with good fuel efficiency for many owners. They continue to make up around 40% of sales in Europe for instance. This relies on AdBlue and the infrastructure is now well established to support all diesel vehicles.

In summary, AdBlue has become integral to operating modern clean diesel engines. It provides an efficient method to make NOx emissions harmless. This keeps diesels compliant with the ever-tighter regulations on exhaust emissions across different world markets. Although invisible to most owners, AdBlue certainly plays a crucial role in today’s automotive landscape.