Date Published: January 27, 2026 | Last Modified: 1 hour ago | 4 minute read | Verified by Mitchell Bazinet at Redwater Dodge

The Ultimate Ram Diesel Winter Guide: Everything You Need to Know About DEF

Does DEF freeze and can it crack my tank?

Does DEF Freeze? (And Will It Damage My Tank?)

The short answer is yes, DEF freezes, but the more important answer is no, it will not crack your tank.

DEF is a mixture of high-purity urea and deionized water. Because of its composition, it begins to crystallize and freeze at approximately -11°C. While that might sound alarming, Ram engineers have already accounted for physics.

When water freezes, it expands. To prevent damage, Ram DEF tanks are designed with specific "expansion room." The tank material and geometry allow the DEF to turn into a solid without putting structural pressure on the reservoir. You can rest easy knowing that a frozen tank does not equal a broken tank.

How the Ram Heated DEF System Works

You might wonder: "If the fluid is frozen, how does the truck run?" Your Ram truck is smarter than the weather. It utilizes an automatic heated DEF system that includes:

A Heated Reservoir: To thaw the bulk fluid.

Heated Delivery Lines: To ensure the fluid can travel to the injector.

Smart Sensors: To monitor the state of the fluid.

The beauty of this system is that it is entirely hands-off. Once you start your engine, the truck begins the thawing process automatically. The truck will not attempt to inject DEF until it has reached the proper operating temperature. This protects your injectors and sensors from being forced to move solid crystals, preventing mechanical failure before it can even start.

What to Do if Your DEF Warning Light Appears

Seeing a warning light on a cold morning can be stressful. If your DEF light illuminates during a cold snap, follow these three steps:

Step 1: Check Your Levels. Ensure you actually have fluid in the tank. It’s easy to forget to top off during a storm.

Step 2: Give it Time. Allow the truck to reach full operating temperature. Often, the light is simply notifying you that the system is still in its thawing cycle.

Step 3: Monitor the Light. If the light remains on long after the truck is warm, it may indicate a fault in the heater element or a sensor. This is when it’s time to visit the pros.

Expert Tip: Winter Maintenance

While the system is robust, we recommend keeping your DEF tank at least half full during the winter months. A fuller tank provides more thermal mass and can actually help the heating system work more efficiently.

If you’re experiencing issues or have more questions about your Cummins engine, don’t hesitate to reach out to the Redwater Dodge service team at 780-942-3629. We're here to keep you on the road, no matter how low the temperature drops.

Additional DEF Questions 

Q1. Can I add anti-freeze or additives to my DEF to keep it from freezing?

A1. Absolutely not. Never add anything to your DEF tank except ISO 22241 certified DEF. Additives can contaminate the SCR (Selective Catalytic Reduction) system, leading to thousands of dollars in repairs and voiding your warranty.

Q2. Does frozen DEF lose its effectiveness once it thaws?

A2. No. One of the great things about DEF is that freezing and thawing does not degrade the quality of the solution. Once it returns to liquid form, it is just as effective at neutralizing NOx emissions as the day you bought it.

Q3. Should I drain my DEF tank if I'm parking the truck for the winter? 

A3. No, there is no need to drain the tank. As long as there is room for expansion (which the tank design ensures), the fluid can stay in the vehicle. However, DEF does have a shelf life, so if the truck sits for over a year, you may want to refresh the fluid.