Does DEF freeze? Yes. Diesel exhaust fluid starts to freeze at around 12°F (minus 11°C), which is a normal winter night in the mountains of West Virginia, western Maryland and Pennsylvania. The good news is that frozen DEF is not ruined, and modern trucks and equipment are built to handle it. What fleets, farms and job sites do need to manage is how DEF is stored, handled and rotated through the cold months, because that is where most winter DEF problems start.
Does DEF freeze: the short answer
DEF is a solution of 32.5% high-purity urea and 67.5% deionized water. That ratio was chosen in part because it has the lowest freezing point of any urea and water mix. Here is what happens in cold weather:
- It freezes at about 12°F. Below that temperature, DEF turns to slush and then solid ice.
- It expands as it freezes. Like water, DEF can expand by up to about 7% when it freezes, so a full container or tank can crack.
- It thaws without damage. When frozen DEF thaws, it does not leave solids behind or lose effectiveness, according to engine maker mtu (Rolls-Royce Power Systems).
- Your vehicle is designed for it. SCR-equipped trucks and equipment use heated DEF tanks and lines, so the engine starts normally and the system thaws DEF as the engine runs.
What to do if DEF freezes in your truck or equipment
- Start and run the engine as usual. The DEF heater will thaw the fluid while you operate.
- Do not add anything to the DEF tank to melt it. Antifreeze, alcohol, fuel additives or tap water will contaminate the fluid and can damage the SCR system.
- Do not top off a frozen tank. Leave room for expansion and fill once the fluid has thawed.
- Watch for warning lights. If a DEF warning stays on after the engine has warmed up, have the heater and sensors checked.
DEF storage temperature and shelf life
Cold does not hurt stored DEF, but heat does. Over time, high temperatures break down urea and shorten shelf life. Industry guidance recommends keeping DEF between about 12°F and 86°F, out of direct sunlight. Properly stored DEF typically lasts about 12 months, while DEF kept at 86°F or higher can last as little as about 6 months, according to Heavy Duty Trucking.
| Storage condition | What happens to DEF | What to do |
|---|---|---|
| Below 12°F | Freezes and expands up to about 7% | Leave headspace in containers and tanks; let it thaw before use |
| 12°F to 86°F | Ideal storage range | Rotate stock and use oldest product first |
| Above 86°F | Urea breaks down faster and shelf life drops | Store in shade or indoors; avoid long storage in hot trailers |
| Direct sunlight | Heat and UV shorten shelf life | Keep jugs, totes and tanks out of direct sun |
Winter DEF storage tips for fleets and farms
- Leave room for expansion. Do not fill outdoor containers or tanks to the top if they could freeze.
- Keep bulk tanks in a protected spot. A heated shop, an insulated enclosure or a tank with a heating system helps keep DEF ready to dispense on the coldest mornings.
- Use dedicated DEF equipment. Pumps, nozzles, funnels and containers that have touched fuel, oil, coolant or tap water will contaminate DEF.
- Keep containers sealed. An open container can pick up dirt, moisture and debris, and evaporation can change the concentration.
- Buy what you will use. Order on a schedule that matches your usage so DEF does not sit through a hot summer after a cold winter.
- Buy from a trusted source. Use DEF that meets API and ISO 22241 requirements. Woodford is an authorized Blue Sky DEF distributor.
Bulk DEF vs. jugs in winter
Packaged DEF is easy to carry in a truck, but jugs left in a cab or bed can freeze, and a half-used jug sitting in a hot cab next summer can lose quality. Bulk DEF stored in an on-site tank gives you more control over temperature, cleaner dispensing and a lower cost per gallon for higher-volume users. For a full comparison, read bulk DEF vs. jugs.
How Woodford supplies DEF
Woodford is a local DEF supplier for fleets, farms and industrial sites across West Virginia and five neighboring states. We supply:
- Packaged DEF in 2.5-gallon containers
- Bulk DEF delivery to on-site storage tanks, on a schedule that matches your usage
- Tanks and dispensing equipment so you never run out
Running diesel equipment through the winter? Our guide to how long diesel fuel can be stored covers on-site fuel storage, and our fleet fueling team can help keep your trucks moving.
Frequently asked questions
At what temperature does DEF freeze?
DEF begins to freeze at about 12°F (minus 11°C). The 32.5% urea concentration gives it the lowest freezing point of any urea and water solution.
Is frozen DEF still good?
Yes. Freezing and thawing do not change DEF’s quality or effectiveness, as long as the container has not cracked or been contaminated.
Can I add antifreeze or water to keep DEF from freezing?
No. Any additive or tap water contaminates DEF and can damage the SCR system. Use DEF exactly as supplied and rely on your vehicle’s built-in heaters.
How long is DEF good for?
Stored between about 12°F and 86°F and out of the sun, DEF typically lasts about 12 months. Storage at 86°F or higher can cut that to roughly 6 months.
Keep your fleet running all winter with Woodford DEF
Woodford is a family-owned, third-generation fuel and lubricants distributor serving fleets, farms and job sites since 1947, and an authorized Blue Sky DEF distributor. Request a DEF quote, open a commercial account, or call us at 1-800-927-3688.
