Updated 2026-11-12
Why heat matters
ISO 22241-3 recommends avoiding prolonged storage above 86°F (30°C). At a constant 86°F, minimum shelf life is about 12 months. At 95°F it is about 6 months, and above that each batch should be tested (ISO 22241-3:2017, Diesel engines NOx reduction agent AUS 32, Part 3: handling, transportation and storage). A tote in direct sun can run much hotter than the air around it.
Practical storage rules
- Shade first. Keep totes and drums indoors or under a roof. A shade structure is cheaper than spoiled fluid.
- Ventilate. Closed metal containers and sheds trap heat.
- Size for turnover. Buy what you will use in a few months, not a year.
- Deliver more often. Smaller, more frequent deliveries keep fluid fresher.
- Check dates. Ask for the fill date on every delivery and use the oldest first.
- Keep it sealed. Open containers lose water and pick up contaminants faster in heat.
Testing DEF that has been hot
A handheld DEF refractometer checks urea concentration. Good DEF reads 32.5%. If fluid has sat hot for months, test it before it goes into a truck.
Lubricants in heat
Oil and grease are less sensitive than DEF, but drums stored outdoors breathe in moisture as they heat and cool. Store drums under cover or on their side with bungs at 3 and 9 o'clock.
Questions
What is the max temperature to store DEF?
ISO 22241-3 recommends avoiding prolonged storage above 86°F (30°C). Short exposures happen, but sustained heat shortens shelf life.
Is DEF hazardous in heat?
DEF is non-flammable. In heat it can release small amounts of ammonia when opened, so open containers in a ventilated area.