Opinion: Ensuring Quality of Diesel Exhaust Fluid Can Help Keep Trucks Running Smoothly

Fleet managers and truck drivers both need to understand that the quality of the diesel exhaust fluid (DEF) going into their vehicles is as important as the quality of the engine oils or fuels used in their vehicles.

DEF is made from a mixture of technically pure urea and purified water and must be handled and stored properly to preserve its quality. This is true for truck drivers filling up on the road and for shops that stock DEF.



One of the main challenges for drivers is knowing the brand of DEF they are being sold, as many fill-up locations don’t identify the manufacturer and brand name on the receipts to their customers. This information is required to be provided when bulk DEF is delivered to the location by many states. Without it, locations cannot provide the information on dispenser receipts.

Drivers accustomed to purchasing DEF in containers should look at the expiration date on the bottle and be sure to use it before this date, as the product has a limited shelf life. If a date is not present, ask for the most recently delivered DEF products.

Storage conditions also impact quality. DEF can be expected to have a minimum shelf life of 12 months or even longer in optimum conditions. Check the label for recommended storage temperatures.

Industry experts recommend that DEF is not stored for too long in a truck once it has been purchased, especially if the storage area in the vehicle is routinely hotter than the recommended storage temperatures displayed on the label.

Purchasing DEF for Shop Use

One common misconception among fleet managers is the belief that if the urea concentration of their DEF is on spec, the DEF meets the required quality. While it is true that the concentration is important, there are many other important quality characteristics built into the ISO 22241 specification. This specification not only includes a list of quality characteristics that DEF must meet, but also includes best practices for the proper transportation, storage and handling of DEF so these properties are not compromised down the supply chain.

Fleet managers responsible for procuring DEF should confirm that their suppliers are providing DEF that meets this ISO quality standard. One way to do this is to ensure that their supplier is providing a Certificate of Analysis with every shipment that addresses all of the quality characteristics that the specification requires.

DEF is composed of 32.5% technically pure urea in pure water. Each of these components is critical to the manufacture of DEF that meets the quality standard. Use of substandard urea (such as agricultural-grade urea commonly used as fertilizer) or use of water derived directly from the public water system without proper treatment can introduce contaminants and metals that are not only detrimental to the life of the selective catalytic reduction (SCR) system but can also affect the SCR system’s ability to reduce harmful NOx emissions.

Managing DEF in Shops

For shops, the handling, storage and dispensing of DEF is important so that off-spec DEF doesn’t reach the marketplace. Temperature during transport or at the point of storage or sale can harm the shelf life of DEF sold in containers. Make sure the stock is rotated to use the oldest product first.

Proper storage temperatures in a shop also is vital. Storing in temperatures above 86 degrees Fahrenheit will limit the shelf life of the DEF over time.

Here are some additional factors to consider in storing and handing DEF:

• Bulk storage tanks should be dedicated for DEF. Don’t switch products in the bulk tank without thoroughly rinsing the tank with distilled or deionized water or on-spec DEF.

• A closed loop system is a fully sealed system that allows bulk containers and drums to be refilled without exposing the DEF to the storage environment. A closed loop system is recommended so contaminants don’t get into the DEF. This is particularly important in a shop or construction site that has dust or dirt in the air.

• Use dedicated equipment for dispensing DEF. Don’t use funnels, pitchers or hoses that are used for other fluids when putting DEF in a tank.

• Anything used for dispensing DEF should be cleaned with distilled or deionized water and followed by a DEF rinse. Don’t use tap water for cleaning.

Ultimately, ensuring the quality of DEF can keep a truck running smoothly, and the proper handling and storage of DEF is vital. Fleet managers and truck drivers should ensure they are using quality DEF to meet the high standards that are required by today’s engine and vehicle manufacturers.

Jeffrey Harmening is Team Lead, Diesel Exhaust Fluid, at the American Petroleum Institute. API is a national trade association that represents all aspects of America’s oil and natural gas industry and has more than 70 years of experience setting engine oil performance standards.