Anyone who keeps a supply of diesel exhaust fluid (DEF) and lives in a climate with very cold winter temperatures must learn how to prevent the fluid from freezing. This begins at a temperature of 12 degrees Fahrenheit. Owners of diesel pickup trucks and cars for personal use usually just fill the fluid container at a service station, but owners of fleets and agricultural enterprises commonly keep a supply on hand where the vehicles are stored or fueled.

Freezing and DEF Lifespan

Freezing generally does not harm this liquid. However, manufacturers recommend not allowing the temperature to get below 12 degrees or the lifespan of DEF can be shortened. The fluid composition changes due to degradation. Sensors inside the vehicle trigger a fault code to display if the quality is low.

Inside the Vehicle

Preventing freezing of this fluid inside the vehicle should not be necessary. The vehicle typically will still start and operate if this happens, and the fluid will thaw relatively quickly. If the temperature gets so cold that the DEF becomes solid like ice instead of slushy, the owner may need to run a heater in the garage. Specialized heaters are available that have been designed to specifically address the problem of DEF freezing.

No Adding of Antifreeze Ingredients

Vehicle owners should not add any type of antifreeze ingredients to the container, as that contaminates the fluid. Although some men and women like to add these substances to their fuel tank, those products should never be placed in a container of DEF. That includes containers inside the vehicle and those in a storage area.

Preventing Problems in the Refill Supply

Preventing freezing in the supply that refills the vehicle containers must be done, though. There’s no way to add frozen liquid to the vehicle container. Another consideration is that freezing causes liquid to expand. Any container that holds DEF during temperatures below 12 degrees must have some space at the top or the container will break. Even metal will break if the ice expands enough. Consider how closed aluminum soda cans burst open in the freezer or inside a vehicle during the winter.