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Everything You Need To Know About DEF

What is DEF?
Diesel Exhaust Fluid (DEF) is a nontoxic solution of 67.5% purified water and 32.5% pure automotive grade urea that is API Certified and complies with ISO 22241-1. DEF is the key element of the Selective Catalytic Reduction (SCR) system used by most medium and heavy-duty diesel engine manufacturers to meet EPA 2010 regulations. When injected into the exhaust stream and passed over a catalyst, Diesel Exhaust Fluid helps convert NOx into nitrogen gas and water vapor – two harmless and natural components of the air we breathe.

A Brief History
The EPA began regulating greenhouse gases from mobile and stationary sources of air pollution under the Clean Air Act (CAA) for the first time on January 2, 2011. NOx reduction is necessary because it contributes to acid rain and smog, making it harmful to our health and our environment. Diesel engines are now required to meet these tighter NOx standards for the US market.

The SCR System
Selective Catalytic Reduction technology is the dominant system to meet these new standards by heavy-duty engine (Class 7-8 trucks) manufacturers. The SCR system works by injecting DEF directly into the exhaust upstream of a catalyst. There, DEF vaporizes and decomposes to form ammonia. The ammonia then works in conjunction with the SCR catalyst to break down NOx into harmless nitrogen and water.  

Drivers must be sure to not run out of DEF in an SCR equipped truck by monitoring the DEF gauge, as the truck will not run without it. The DEF tank fill opening is designed to accommodate a DEF fill nozzle to ensure only DEF is put into the tank and cannot be mistaken as diesel.

DEF Storage
Quality control is very important in the handling and storage of DEF to ensure the SCR system stays functioning properly. DEF should always be stored in a cool, dry, well-ventilated area – preferably away from direct sunlight. Do not store diesel exhaust fluid in carbon steel, aluminum, copper, or zinc because it will corrode these metals. The recommended temperature range for storage is 12° - 86° F, but temporary exposure to warmer temperatures will not degrade its quality or performance. If DEF is stored at approximately 75°F, the shelf life should be two years long.

DEF dust can contaminate the fluid around the area where DEF is added to the system so be sure to keep this area clean and free of debris. It is crucial that the 32.5% urea solution remains at this ratio because it provides the lowest freezing point for DEF which is near 12°F. Additionally, SCR systems are calibrated to the 32.5 percentage. It is unlikely for DEF to freeze while a vehicle is running as the SCR technology heats the DEF tank and supply lines. DEF is more likely to freeze when the vehicle is not being operated, but the vehicle will start up and run as normal. Once the vehicle is started, the SCR system will melt the frozen DEF quickly and the vehicle will not be impacted. DO NOT ADD OTHER CHEMICALS TO KEEP DEF FROM FREEZING. If something is added, it can ruin the solution and may even damage SCR components. 

Equipment and Availability
An experienced DEF supplier, such as Shrader Tire & Oil understands important DEF issues and can be flexible in meeting your DEF needs. We have the expertise, regional supply and customized distribution solutions to help you achieve the right DEF supply strategy for your application.

Allow Shrader to assist you with a custom DEF solution for your fleet while reducing maintenance costs and creating less harmful emissions in the atmosphere. Shrader carries Victory Blue DEF which is API certified. We offer DEF in bulk, 330 gallon totes, 55 gallon drums, and 2.5 gallon jugs. Look to Shrader for DEF distribution equipment including hand pumps, reels, and electronically metered pumps.


Kyle Perna, DEF Sales Specialists
(419) 351-5770