what temp does def freeze

Diesel Exhaust Fluid (DEF) starts to freeze at about 12 °F, which is roughly −11 °C.

Quick Scoop: What temp does DEF freeze?

The short answer

• DEF freezing point: about 12 °F (−11 °C).

• Below this temp, the water in the mix turns to ice and the DEF becomes solid or slushy.

DEF is a mix of 32.5% urea and 67.5% deionized water, and that specific ratio is what makes its freezing point sit right around 12 °F (−11 °C).

What happens when DEF freezes?

• The fluid solidifies in the tank and lines when ambient temperature drops below about 12 °F (−11 °C).

• The water portion expands as it freezes, so an overfilled DEF tank can crack or get damaged as the ice pushes on the walls.

• Modern trucks are designed so the DEF system can thaw itself with built‑in heaters in the tank and lines once the engine is running.

A typical real‑world scenario: a truck parked outside overnight at −20 °C will usually have a frozen DEF tank in the morning; after startup, the system slowly warms and melts the DEF so emissions controls come online again.

Is frozen DEF ruined?

• Freezing does not permanently damage DEF quality; once thawed, it works the same as before.

• The main risk is physical damage to storage containers, tanks, or pumps from the expansion of ice, not chemical breakdown of the fluid itself.

Can you add anything to stop DEF from freezing?

• You should not add antifreeze, alcohol, or any other additive to DEF to lower its freezing point.

• Additives contaminate the fluid and can damage the SCR system or make it fail emissions requirements.

Manufacturers intentionally keep DEF’s composition standardized year‑round and rely on heating systems and proper storage instead of changing the formula for winter.

Key facts about DEF and temperature (SEO‑friendly)

• DEF freezes at about 12 °F (−11 °C).

• Ideal storage is generally between 12 °F (−11 °C) and about 86 °F (30 °C) for shelf life and performance.

• Multiple freeze–thaw cycles do not harm DEF as long as it stays uncontaminated.

• The real “problem” in winter is often frozen pumps, lines, or cracked containers, not the DEF chemistry itself.

“What temp does DEF freeze?”
Real‑world answer from truckers and fleets in cold regions: expect frozen DEF right around −11 °C (12 °F), and plan your storage and parking with that number in mind.

Simple HTML table for quick reference

html

<table>
  <thead>
    <tr>
      <th>Property</th>
      <th>Value</th>
      <th>Notes</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>DEF freezing point</td>
      <td>≈ 12 °F (−11 °C)</td>
      <td>Standard 32.5% urea / 67.5% water mix.[web:1][web:3][web:5]</td>
    </tr>
    <tr>
      <td>Effect of freezing</td>
      <td>Solid/slushy DEF, volume expansion</td>
      <td>Can crack overfilled tanks or containers.[web:1][web:10]</td>
    </tr>
    <tr>
      <td>After thawing</td>
      <td>Still usable</td>
      <td>Does not lose effectiveness if uncontaminated.[web:2][web:3][web:5]</td>
    </tr>
    <tr>
      <td>Additives allowed?</td>
      <td>No</td>
      <td>Do not add antifreeze or chemicals; keeps DEF and SCR system healthy.[web:1][web:2][web:3]</td>
    </tr>
  </tbody>
</table>

TL;DR: DEF freezes at around 12 °F (−11 °C), but freezing doesn’t ruin it—just avoid overfilling tanks and never add antifreeze or other chemicals.

Information gathered from public forums or data available on the internet and portrayed here.