Temperature Effect on Diesel Exhaust Fluid

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Diesel exhaust fluid, or DEF, is a key component in the selective catalytic reduction, or SCR system for modern diesel engines. DEF breaks down harmful NOx (Nitrous Oxide) emissions that come from a diesel vehicle’s exhaust stream. It also helps keep vehicles’ emissions compliant. DEF is a non-toxic, non-hazardous, and non-flammable blend of urea and deionized water. Because it is made of water, diesel exhaust fluid can freeze if stored in cold temperatures for a long time. Additionally, high temperatures can also have a negative impact on shelf life.

At What Temperature Does DEF Freeze?

DEF freezes at 12 degrees Fahrenheit due to the ratio of urea (a synthetic nitrogen compound) to deionized water. The mixture contains a 32.5% urea concentration, which lowers the freezing point of the liquid. This percentage of urea is critical to the function of the SCR system so that emissions are effectively reduced while a diesel engine is running. The 32.5% urea concentration allows for both parts of the compound to freeze at the same temperature, and it also helps them thaw at the same rate without degrading the product.

Diesel exhaust fluid can freeze both in storage containers and in a vehicle’s tank itself. However, freezing will not compromise the quality of the DEF. If DEF freezes in the tank, it will quickly thaw as temperatures rise and it will not affect how well the vehicle operates. No additives are needed to help diesel fluid thaw in freezing temperatures. In fact, additives will corrupt the purity of the fluid and can negatively impact the SCR system.

Keep in mind that if the storage temperature is consistently below 12 degrees Fahrenheit, diesel exhaust fluid can expand by up to 7%, which can cause damage to storage containers.

Can I Winterize Diesel Exhaust Fluid?

No additives should ever be added to diesel fluid to winterize it. The DEF mixture depends on a strict ratio of urea to deionized water. Also, it has to meet ISO 22241 specifications, and additives can negatively impact that delicate balance. Contaminants can cause damage to the SCR system and also affect the mixture’s ability to properly break down NOx in emissions. The selective catalytic reduction, or SCR system, is designed to provide proper heating to the DEF tank and lines while in operation. This helps to convert any frozen fluid into liquid form without impacting vehicle operation.

Proper storage and handling of DEF is the best way of managing it in cold weather. It should be stored above 12° F. When DEF is stored at temperatures outside of the recommended range, it will decrease the shelf life. On the bright side, it will not compromise the quality.

What Are the Effects of Higher Temperatures on Diesel Exhaust Fluid?

Although the quality and efficiency of the DEF aren’t impacted by high temperature, it can impact shelf-life. Because diesel exhaust fluid is comprised of 67.5% deionized water, there is a slight concern for evaporation. However, diesel exhaust fluid is typically only at risk of evaporation when stored at temperatures above 86 degrees Fahrenheit for extended periods of time.

In general, there is no significant risk of evaporation with DEF even in high temperatures. That said, the primary way you can avoid overheating is to utilize storage tanks and keep totes out of direct sunlight.

What Is the Shelf Life of DEF?

The American Petroleum Institute (API) recommends storing DEF in a cool, dry place between 12° F and 86° F in order to take full advantage of the two-year shelf life. Luckily, many storage containers are now designed to provide a temperature-controlled environment for stored diesel fluid.

It’s also important that containers for storage are clearly coded with a manufacturing date to help determine the shelf life and if it is still appropriate for use in your diesel vehicle.

Of course, the best piece of advice we can offer when you have questions about DEF storage is to talk to your supplier.

Learn more about proper DEF storage from your Retif Oil & Fuel representative.


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