Diesel exhaust fluid, or DEF, is not only required in most diesel engines in order to reduce NOx emissions, but it also helps improve your engine’s fuel efficiency and performance. It’s important to store it properly, especially during the winter, to ensure it maintains its purity and is able to carry out its purpose. Here are some tips recommended by DEF manufacturers and suppliers for storing DEF during the winter.

Prevent Freezing

DEF is made mostly of water, with the other part being urea. That means that DEF will freeze if it’s stored somewhere that’s exposed to freezing temperatures. However, its freezing point isn’t the same as water because of the urea, so it typically won’t freeze until the temperature is lower than 12 degrees Fahrenheit. If the DEF freezes in your vehicle’s tank, there’s no need to worry because it will quickly thaw and the quality is unaffected. But it’s still a good idea to store DEF in a temperature-controlled environment when possible because freezing can have other effects.

Expansion

One reason DEF distributors recommend you prevent the solution from freezing is that, like water, the DEF will expand when it freezes–up to 7%. This can damage the storage tank, especially if the tank is full or nearly full when the freezing occurs. If the DEF is at risk of freezing it’s a good idea to make sure the tank isn’t completely full to prevent damage to the tank from expansion.

Avoid Additives

Even though the vehicle will start without trouble if the DEF freezes, some people are tempted to add solutions to the DEF to keep it from jelling, or to raise the freezing point. However, it’s important to note that DEF must remain pure for it to work correctly in the SCR system. Even if the DEF in the storage tank is frozen solid the SCR system has a heating element that will quickly thaw the DEF so that it’s able to liquefy and resume working as it should.

Storage Containers

If you’re storing extra DEF, be sure to use HDPE plastic containers or stainless steel. DEF is slightly corrosive and may corrode other types of metals, which results in contamination and keeps the DEF from working as well as possible. Contact your local DEF distributor for more helpful tips.