Updated 2026-11-12
DEF shelf life table
The handling and storage standard for DEF, ISO 22241-3, gives minimum shelf life by constant storage temperature:
| Constant storage temperature | Minimum shelf life |
|---|---|
| At or below 50°F (10°C) | 36 months |
| At or below 77°F (25°C) | 18 months |
| At or below 86°F (30°C) | 12 months |
| At or below 95°F (35°C) | 6 months |
| Above 95°F (35°C) | Test the batch before use |
Source: ISO 22241-3:2017, Diesel engines NOx reduction agent AUS 32, Part 3: handling, transportation and storage. Shelf life counts from the production date of the batch, so ask for the fill or batch date.
What happens when DEF goes bad
DEF is 32.5% urea in deionized water. Over time, and faster in heat, the urea breaks down and releases ammonia, and the concentration drifts out of spec. Out-of-spec fluid can trigger warning lights, reduce SCR performance and, in some engines, cause a power derate.
Signs your DEF may be out of spec
- It is past the shelf life for the temperature it was stored at
- It smells strongly of ammonia when opened
- It is cloudy, colored or has particles (good DEF is clear)
- White crystals have formed around caps and fittings (some crystal at a fitting is normal, crystals in the fluid are not)
A refractometer reading confirms concentration. Good DEF reads 32.5% (allowed range about 31.8 to 33.2%).
Does freezing ruin DEF?
No. DEF freezes at about 12°F (-11°C). It expands about 7% when frozen, so leave headroom, but a freeze and thaw does not change its quality.
How to make DEF last
- Store it out of direct sun, ideally indoors or under cover
- Keep containers sealed between uses
- Buy the package size you will use inside the shelf life for your climate
- Use only dedicated, DEF compatible pumps and containers
Planning storage in the South? Read DEF storage in hot climates.
Questions
How long does DEF last in a truck tank?
The same temperature rules apply. Tanks on trucks see heat from the sun and engine, so fluid that sits for months in summer can degrade faster than fluid in a cool shop.
Can I use DEF that froze?
Yes. Once it thaws completely it is fine to use.