
Why Diesel Cars Need AdBlue: How Often to Refill and What Happens If You Stop Using It
With environmental concerns growing across the globe, various regulations have been introduced to reduce harmful emissions from vehicles. Diesel engines, which produce more nitrogen oxides (NOx) than their petrol counterparts, have faced increasing scrutiny.
To meet stringent emissions standards, manufacturers have turned to a solution called AdBlue. AdBlue plays a crucial role in diesel engine operation, especially in modern vehicles.
This article will explore why diesel cars need AdBlue, how often you should top it up, and the consequences of not using AdBlue.
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What is AdBlue, and How Does It Work?
AdBlue is a fluid consisting of deionized water (67.5%) and urea (32.5%). It is not a fuel additive; instead, AdBlue is stored in a separate tank in diesel vehicles equipped with Selective Catalytic Reduction (SCR) systems. The SCR technology uses AdBlue to convert harmful nitrogen oxides (NOx), produced during diesel combustion, into harmless nitrogen (N2) and water (H2O). This chemical reaction significantly reduces the NOx emissions that contribute to air pollution and smog.
How AdBlue Works in the SCR System:
- AdBlue Injection: AdBlue is injected into the exhaust system, not into the engine itself. It is sprayed into the exhaust stream just ahead of the catalytic converter.
- Chemical Reaction: When the high temperatures of the exhaust gases meet AdBlue, it breaks down into ammonia (NH3) and carbon dioxide (CO2).
- NOx Reduction: The ammonia reacts with nitrogen oxides (NOx) in the catalytic converter, transforming them into nitrogen and water vapour, both of which are harmless to the environment.
The use of AdBlue helps diesel vehicles meet Euro 6 emissions standards, which aim to reduce harmful pollutants and make diesel engines cleaner.

Why Do Diesel Cars Need AdBlue?
Diesel engines produce more NOx compared to petrol engines due to their higher combustion temperatures and pressures. NOx gases are a major cause of air pollution, contributing to health problems such as respiratory issues and environmental damage, including acid rain.
To comply with emissions regulations like Euro 6 (introduced in 2015), which focus on reducing NOx emissions, diesel engines need to incorporate technology that mitigates these pollutants. The SCR system, with AdBlue, is the most efficient way to meet these requirements while still maintaining the fuel efficiency and torque benefits of a diesel engine.
Without SCR and AdBlue, modern diesel cars would struggle to meet the legal emission limits, leading to potential bans in certain regions, higher taxes, or hefty penalties for manufacturers and owners.
How Often Do You Need to Refill AdBlue in a Diesel Car?
The frequency of refilling AdBlue depends on several factors, including the make and model of the vehicle, driving conditions, and driving habits. Typically, the average range for a full AdBlue tank can be anywhere from 8,000 to 16,000 kilometres.
However, the rate at which AdBlue is consumed can vary:

- Driving Conditions: City driving, with frequent stops and starts, can result in higher AdBlue consumption compared to highway driving.
- Driving Style: Aggressive driving that involves rapid acceleration and higher engine load may increase AdBlue usage.
- Vehicle Model: Different vehicles have varying tank sizes and SCR efficiency, which affects how often AdBlue needs to be topped up.
Indicators of Low AdBlue Levels:
- Modern diesel vehicles equipped with AdBlue systems will notify the driver when the AdBlue tank is running low. These warnings typically appear well before the tank is empty, giving drivers ample time to refill.
- The dashboard will usually display a warning light or a message stating how many kilometres you can drive before AdBlue runs out.
It is crucial to pay attention to these warnings. In many cases, if the AdBlue tank becomes empty, the car may refuse to start until it has been refilled.
How to Refill AdBlue:
- AdBlue is available at service stations, automotive retailers, or online. It is sold in containers ranging from 5 litres to 20 litres, and some fuel stations even have dedicated AdBlue pumps for larger vehicles.
- If you’re in Australia and managing fleets or need bulk quantities, EcoBlue Bulk AdBlue offers an excellent solution for purchasing AdBlue in large volumes. This option is particularly beneficial for businesses looking to ensure consistent supply without frequent refills.
- Refilling AdBlue is usually straightforward. The tank is often located near the fuel cap or in the boot of the vehicle. Be sure to avoid contaminating the AdBlue tank with diesel or other substances, as this can damage the SCR system.
What Happens if You Stop Using AdBlue?
Since AdBlue is integral to the SCR system in modern diesel vehicles, failing to use it or running out can lead to a series of issues.
- Emission Standards Violation: If you stop using AdBlue, your vehicle will no longer meet the emissions standards it was designed to comply with. This means your car will be emitting higher levels of nitrogen oxides (NOx), contributing to air pollution and potentially causing your vehicle to fail emissions tests in countries with strict regulations.
- Performance Limitations: Many modern diesel vehicles have built-in safety systems to prevent driving without AdBlue. If the AdBlue tank runs dry, the car’s ECU (engine control unit) may limit engine performance. The vehicle may enter “limp mode,” restricting speed and power to prevent further damage and higher emissions.
- Engine Won’t Start: If AdBlue runs out entirely, many vehicles will refuse to start. This is a safeguard to ensure the car doesn’t operate while emitting excessive NOx. In this case, refilling the AdBlue tank is the only way to get the car running again.
- Potential Damage to the SCR System: While running out of AdBlue temporarily won’t cause permanent damage, continuously neglecting to refill it can place strain on the SCR system. The system is designed to operate with AdBlue, and its absence can cause malfunctions, potentially leading to costly repairs down the line.
- Fines and Penalties: In countries with strict emissions control regulations, driving a car without AdBlue could lead to fines or penalties. Regular emission tests may also be required to ensure compliance, and failing these tests due to insufficient AdBlue usage could result in costly repairs or legal consequences.

Frequently Asked Questions (FAQs)
Q: Can I Use Water Instead of AdBlue?
No, using water instead of AdBlue will not work. AdBlue is a specific solution of urea and deionized water, and water alone cannot facilitate the necessary chemical reactions to reduce NOx emissions. Using anything other than AdBlue can damage the SCR system.
Q: Is AdBlue Expensive?
AdBlue is generally affordable. In Australia, for example, the price of AdBlue in 2024 averages around AUD 1.50 to AUD 2.50 per litre, depending on the location and supplier. Considering that a full tank of AdBlue lasts between 8,000 and 16,000 kilometres, the cost is relatively low compared to other vehicle maintenance expenses.
Q: Can I Overfill the AdBlue Tank?
Overfilling the AdBlue tank is generally not recommended. Most systems are designed to handle specific quantities, and overfilling could lead to spills or damage to the SCR components. Always follow the manufacturer’s recommendations for refilling.
Q: What Should I Do if I Accidentally Put AdBlue in the Fuel Tank?
If AdBlue is accidentally poured into the diesel fuel tank, do not start the engine. Starting the engine could cause severe damage to the fuel system. You should contact a professional mechanic to drain and clean the fuel tank immediately.
Conclusion
AdBlue is essential for modern diesel vehicles with SCR systems, allowing them to meet stringent emissions regulations while still delivering the power and fuel efficiency associated with diesel engines. Regularly topping up AdBlue is crucial for maintaining the vehicle’s emissions standards and preventing any operational issues. Ignoring AdBlue requirements can result in performance limitations, engine failures, and significant repair costs.
Diesel car owners should be diligent about checking AdBlue levels, especially during long trips or before emissions tests, to avoid any disruptions. Overall, the relatively low cost of AdBlue, combined with its environmental benefits, makes it a necessary and worthwhile addition to diesel vehicle maintenance.