Tips for Purchasing and Storing DEF to Preserve Quality

How you purchase, handle and store API certified diesel exhaust fluid impacts its quality and its ability to keep equipment running smoothly


Diesel Exhaust Fluid (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 drivers filling up on the road and for shops that stock DEF.

On the road, one of the main challenges for drivers is the knowing the brand of DEF they are being sold as many fill up locations don’t identify the manufacturer and brand name from bulk dispensers, despite regulations in many states that require this information. It is difficult for drivers to confirm they are buying DEF that is licensed by API’s Diesel Exhaust Fluid Certification Program unless it is marked. Many diesel engine manufacturers recommend that drivers use API-licensed DEF.

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 have an impact on its 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. API recommends that you don’t store if for too long in your truck once you purchase it, especially if the storage area in the vehicle is routinely hotter than the recommended storage temperatures displayed on the label. Be sure to look for the API certification mark on the bottle as well.

Purchasing DEF for shop use

API has found that the biggest misconception by fleet managers is the belief that if the urea concentration of their DEF is on spec, then the DEF meets the required quality. While it is absolutely true that the concentration is very important, there are many other important quality characteristics built into the ISO 22241 specification.

DEF is composed of 32.5% technically-pure urea in pure water. Each of these components are critical to the manufacture of DEF that meets the quality standard. Use of sub-standard 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.

Fleet managers responsible for procuring DEF should confirm that their suppliers are providing DEF that meets the ISO quality standard. One way to do this is to ensure that their supplier is providing a Certificate of Analysis (or Quality) with EVERY shipment that addresses all of the quality characteristics that the specification requires. Fleets and drivers can check to see if the DEF they are buying is licensed through API’s real-time directory of licensees on the API website.

Managing DEF in shops

For shops, the handling, storage and dispensing of DEF is very 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 is also vital. Storing in temperatures above 86 degrees Fahrenheit will limit the shelf life of the DEF over time. Some additional things to consider in storing and handing DEF include the following:

  • Bulk storage tanks should be dedicated for DEF. Don’t switch products in the bulk tank without thoroughly rinsing the tank with distilled or de-ionized water or on-spec DEF.
  • A closed loop system for transferring DEF from a drum or bulk tank 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, hoses, etc. that are used for other fluids when putting DEF in a tank.
  • Anything used for dispensing DEF should be cleaned with distilled or de-ionized water and followed by a DEF rinse. Don’t use tap water for cleaning.

For shops and drivers, it’s important to know what you are putting into your DEF tank. The quality of the DEF going into your vehicle is as important as the quality of the engine oils or fuels used in your vehicles. Use of API-licensed Diesel Exhaust Fluid will ensure that the DEF meets the high standards required by engine and vehicle manufacturers.

The American Petroleum Institute (API) is the only national trade association representing all facets of the natural gas and oil industry. API was formed in 1919 as a standards-setting organization. In its first 100 years, API has developed more than 700 standards to enhance operational and environmental safety, efficiency and sustainability.