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What is Diesel Exhaust Fluid? Is DEF and Ecolube AdBlue the Same? What Happens If You Run Out of DEF?

What is Diesel Exhaust Fluid? Is DEF and Ecolube AdBlue the same? What happens if you run out of DEF? Read this to learn more

Modern diesel engines rely heavily on Diesel Exhaust Fluid (DEF) and AdBlue to meet stringent environmental standards and maintain performance. Often used synonymously, these two actually refer to the same emission-reducing solution.

This article would look into DEF and AdBlue, explaining their functions, and highlighting both their similarities and differences. Additionally, it offers handy advice for handling DEF in your vehicle, ensuring it operates efficiently and eco-consciously.

What is Diesel Exhaust Fluid?

Diesel Exhaust Fluid, often abbreviated as DEF, is a crucial component in the operation of modern diesel engines, especially those that meet the stringent emission standards set by environmental regulations. If you own a diesel vehicle or work in an industry that uses diesel-powered machinery, understanding DEF is essential. Let’s break down what DEF is, why it’s important, and how it works.

What is DEF Made Of?

DEF is a non-toxic, colourless, and odourless liquid composed of 32.5% high-purity urea and 67.5% deionized water. Urea is a compound of nitrogen that turns into ammonia when heated. The specific concentration of urea is critical because it ensures optimal performance in reducing emissions.

How Does DEF Work?

DEF is used in a system called Selective Catalytic Reduction (SCR), which is installed in many modern diesel engines. The SCR system is designed to reduce the amount of harmful nitrogen oxides (NOx) emitted from the exhaust. Here’s a step-by-step look at how the process works:

  1. Injection into the Exhaust Stream: DEF is stored in a separate tank on the vehicle. When the engine is running, DEF is injected into the exhaust stream before it reaches the SCR catalyst.
  2. Chemical Reaction: Once injected, the DEF heats up and breaks down into ammonia (NH3) and carbon dioxide (CO2). The ammonia then reacts with the nitrogen oxides in the exhaust gas.
  3. Reduction of Emissions: This reaction converts the harmful NOx into harmless nitrogen (N2) and water vapour (H2O), which are then released into the atmosphere.

This process significantly reduces the emission of NOx, which are major pollutants that contribute to smog, acid rain, and respiratory problems in humans.

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Why is DEF Important?

  1. Environmental Protection: By reducing NOx emissions, DEF helps in protecting the environment and improving air quality. This is particularly important in urban areas where air pollution can be a serious health hazard.
  2. Regulatory Compliance: Many countries have strict emission standards for diesel engines. Using DEF and SCR technology allows manufacturers to comply with these regulations, avoiding hefty fines and legal issues.
  3. Engine Efficiency: Vehicles equipped with SCR systems and using DEF tend to have better fuel efficiency and performance. This is because the engine can be tuned for maximum efficiency and power output without having to worry as much about NOx emissions.

Using and Handling DEF

  1. Storage: DEF should be stored in a cool, dry place away from direct sunlight. It can freeze at temperatures below 12°F (-11°C), but it will thaw without losing its effectiveness.
  2. Shelf Life: DEF has a shelf life of about two years if stored properly. Always check the expiration date on the container before using it.
  3. Handling: DEF is safe to handle, but it should be kept clean to avoid contamination. Contaminants can cause the SCR system to malfunction. Use dedicated equipment when refilling the DEF tank to maintain purity.
  4. Refilling: Many vehicles have a dedicated DEF gauge or warning light that alerts the driver when the fluid level is low. It’s important to refill the DEF tank promptly to ensure continuous operation of the SCR system.

Is DEF and Ecolube AdBlue the Same?

Yes, DEF (Diesel Exhaust Fluid) and Ecolube AdBlue are essentially the same thing, though there are some differences in terms of terminology and application. Here’s a clear breakdown of what DEF and Ecolube AdBlue are, how they relate to each other, and what you should know about them:

What is DEF?

Diesel Exhaust Fluid (DEF) is a solution used in modern diesel engines to reduce nitrogen oxides (NOx) emissions. It is made up of 32.5% high-purity urea and 67.5% deionized water. DEF is injected into the exhaust stream of diesel engines where it helps to convert harmful NOx emissions into harmless nitrogen and water vapour through a process called Selective Catalytic Reduction (SCR).

What is Ecolube AdBlue?

Ecolube AdBlue is a brand name for a type of DEF, Ecolube is a leading supplier of AdBlue in Australia. It is a specific product that meets the same standards as DEF and is used for the same purpose. Ecolube AdBlue is produced according to strict guidelines and specifications to ensure it performs effectively in SCR systems.

Key Similarities

  • Composition: Both DEF and Ecolube AdBlue contain 32.5% urea and 67.5% deionized water. This standardized mixture is crucial for their effectiveness in reducing NOx emissions.
  • Function: Both DEF and Ecolube AdBlue are used in the SCR technology of diesel engines to convert NOx into nitrogen and water vapour.
  • Usage: Ecolube AdBlue and DEF are used interchangeably in vehicles and machinery that require DEF for emission control.

Key Differences

  • Terminology: Ecolube AdBlue is the brand name of a leading AdBlue supplier in Australia and New Zealand that is certified by the German Association of the Automotive Industry (VDA). DEF is a more generic term that refers to any product meeting the ISO 22241 standard for the DEF solution.
  • Brand vs. Generic: Ecolube AdBlue is just one brand of DEF, but there are many other brands of DEF available on the market. All DEF products, regardless of brand, must meet the ISO 22241 standard to ensure they are suitable for SCR systems.

Choosing Between DEF and AdBlue

When it comes to choosing between DEF and AdBlue, you essentially have the same product, but there are some considerations:

  • Certification: Make sure that any DEF or AdBlue product you purchase meets the ISO 22241 standard. This certification ensures that the product is of high quality and suitable for SCR systems.
  • Availability: AdBlue may be more widely available in some regions or at specific retailers. However, as long as the DEF you purchase meets the ISO 22241 standard, it will perform the same function as AdBlue.

How to Use DEF and AdBlue

  1. Check Levels Regularly: Use your vehicle’s DEF gauge or dashboard warning light to monitor DEF levels. Most vehicles will alert you when DEF is low, giving you time to refill it.
  2. Refill When Needed: Refill DEF when the warning light comes on or when the DEF gauge shows low levels. DEF is usually available at auto parts stores, service stations, and online.
  3. Proper Storage: Store DEF in a cool, dry place away from direct sunlight. It can freeze at temperatures below -11°C, but it will thaw and remain effective once warmed up.
  4. Handle with Care: DEF is safe to handle, but it should be kept clean and free from contaminants to avoid damaging the SCR system.

What Happens If You Run Out of Diesel Exhaust Fluid?

Running out of Diesel Exhaust Fluid (DEF) can have several consequences for both your vehicle’s operation and its compliance with emission regulations. Here’s what you can expect if your DEF tank runs dry:

Immediate Effects on the Vehicle

  1. Warning Indicators: Modern diesel vehicles are equipped with sensors that monitor DEF levels. As the DEF level gets low, warning lights or messages will appear on the dashboard. These warnings typically give you ample time to refill the DEF tank before it runs completely dry.
  2. Reduced Performance: If you ignore the initial warnings and continue driving until the DEF tank is empty, your vehicle will likely enter a “limp mode.” This is a protective measure designed to reduce the engine’s performance to limit emissions. In limp mode, the vehicle’s speed and power will be significantly reduced, making it challenging to drive normally.
  3. Engine Start Prevention: Some vehicles have systems in place that will prevent the engine from starting once the DEF tank is empty. This is to ensure that the vehicle does not operate without the necessary emissions control in place. You will need to refill the DEF tank to restart the engine.

Long-term Consequences

  1. Increased Emissions: Without DEF, the Selective Catalytic Reduction (SCR) system cannot function properly. This means your vehicle will emit higher levels of nitrogen oxides (NOx), which are harmful pollutants. Increased NOx emissions can contribute to environmental pollution and health issues.
  2. Regulatory Non-compliance: Many regions have strict emission standards that vehicles must meet. Operating a vehicle without DEF can result in non-compliance with these regulations. This can lead to fines, penalties, or legal issues, especially for commercial vehicles subject to regular inspections.
  3. Potential Damage to the SCR System: Continuously running your vehicle without DEF can cause long-term damage to the SCR system. This system is designed to operate with DEF, and without it, the catalyst and other components can become damaged, leading to costly repairs.

Preventive Measures

  1. Regular Checks: Make it a habit to regularly check your DEF levels, especially before long trips. Many vehicles have a DEF gauge on the dashboard for easy monitoring.
  2. Keep Spare DEF: Carry a spare container of DEF in your vehicle, particularly if you are travelling in areas where DEF might not be readily available.
  3. Service Intervals: During routine maintenance and servicing, ensure that your DEF tank is topped up. Many service centres will check and refill DEF as part of their standard service packages.
Close up man filling a diesel engine fluid from canister into the tank of blue car. Diesel exhaust fluid for reduction of air pollution. Environmental friendly and eco solution

How Often Do You Put DEF in a Diesel?

How often you need to add Diesel Exhaust Fluid (DEF) to your diesel vehicle depends on several factors, including the vehicle’s make and model, driving conditions, and how much you drive.

General Rule of Thumb

In general, DEF is used at a ratio of about 2-3% of the diesel fuel you consume. This means that for every 100 litres of diesel fuel, you will need about 2-3 litres of DEF. This ratio can vary based on your specific vehicle and driving conditions, but it gives you a good idea of how often you might need to refill DEF.

Typical DEF Refill Intervals

  1. Every 480-800 Kilometers: Most diesel vehicles will require DEF refills approximately every 480-800 kilometres. This can vary depending on how much DEF you use relative to your diesel fuel consumption. For vehicles with larger DEF tanks or those driven under less demanding conditions, you might need to refill less frequently.
  2. Every Few Weeks to Months: If you drive regularly, you might need to add DEF every few weeks to a couple of months. For instance, if you drive 1,600 kilometres per week, you might need to refill DEF about every 2-3 weeks.

How to Monitor DEF Levels

  1. Dashboard Warning Lights: Most modern diesel vehicles have a DEF level gauge on the dashboard. It will show the current DEF level and alert you when it’s getting low. Pay attention to these warnings to avoid running out of DEF.
  2. DEF Gauge: Some vehicles also have a dedicated DEF gauge that shows how much DEF is left in the tank. This can help you plan your refills in advance.

Factors Affecting DEF Consumption

  1. Driving Conditions: Heavy loads, frequent stops and starts, and driving in extreme temperatures can increase DEF consumption. For example, if you’re towing a trailer or driving up steep hills, you may need to refill DEF more often.
  2. Vehicle Type: Different vehicles have different DEF tank sizes and consumption rates. Larger vehicles or those with bigger engines might require more DEF compared to smaller passenger vehicles.
  3. Engine Efficiency: Newer engines with advanced emissions systems might use DEF more efficiently, meaning you might not need to refill as often.

Tips for Managing DEF

  1. Check Regularly: Make it a habit to check your DEF levels during routine maintenance or before long trips. Keeping an eye on your DEF levels can prevent you from running out unexpectedly.
  2. Keep Spare DEF: It’s a good idea to carry a spare container of DEF in your vehicle, especially if you travel to remote areas where DEF might not be readily available.
  3. Buy in Bulk: If you use a lot of DEF, buying in bulk can save you money. DEF is available in various sizes, including jugs, pails, and drums.
  4. Store Properly: DEF should be stored in a cool, dry place away from direct sunlight. It can freeze at temperatures below -11°C, but it will thaw and remain effective once it returns to a liquid state.

When to Refuel DEF

Here’s a simple checklist for when to refuel DEF:

  • Check the DEF gauge or dashboard light regularly to see if it’s low.
  • Refill DEF when the warning light turns on or when the gauge shows low levels.
  • Keep track of your driving habits and be aware that demanding driving conditions might lead to more frequent DEF refills.


To wrap up, DEF and AdBlue are fundamentally the same solution, designed to help diesel engines meet modern emission standards through the SCR system. While AdBlue is a brand name for DEF, both serve the same critical function of converting NOx emissions into harmless substances.

Keep your DEF tank filled, handle the fluid properly, and stay informed to keep your engine in top shape and contribute to a cleaner environment.

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