DEF (Diesel Exhaust Fluid) is a carefully blended solution of 32.5% urea and deionized water. It’s used with Selective Catalytic Reduction (SCR) systems on diesel vehicles and equipment to help treat exhaust and meet emissions requirements. DEF is stored in a separate tank and is metered into the exhaust stream—it's not a fuel and doesn’t go in the diesel tank.

• Works only with SCR-equipped diesel engines and machinery.
• Commonly available in 2.5-gallon jugs, larger drums, and bulk totes.
• Use DEF-compatible pumps, nozzles, and hoses to avoid contamination.
• Check your owner’s manual for the correct fill location and fluid specifications.

On most modern diesels that use SCR, the vehicle expects DEF to be present. Operating without DEF can trigger warnings and may lead the system to reduce power or limit speed to encourage a refill, depending on the manufacturer’s design. Some vehicles may even prevent a restart after several key cycles if the DEF tank is empty.

• Expect dashboard alerts as DEF levels drop.
• Power or speed may be reduced to protect the system.
• Restart restrictions are possible on some models.
• Always follow your owner’s manual for specific behavior and guidance.

Keeping a DEF jug on hand can help you avoid interruptions, but results vary by vehicle and conditions.

DEF works alongside an SCR system to treat exhaust after combustion. It’s not mixed with diesel fuel.

1. DEF is stored in its own tank and kept separate from diesel.
2. A dosing unit injects small amounts of DEF into the hot exhaust stream.
3. Heat converts DEF into ammonia, which reacts in the SCR catalyst.
4. This reaction helps convert certain exhaust gases into nitrogen and water vapor.
5. Sensors and controls adjust dosing based on operating conditions.

For clean handling, use DEF-dedicated pumps and nozzles and avoid cross-contamination. Always fill through the DEF port specified by your vehicle’s manual, not the diesel fuel cap.

The right size depends on how often you drive, your storage space, and how you dispense DEF.

• 2.5-gallon jugs: Handy for personal vehicles and occasional top-offs; easy to carry and store.
• 55-gallon drums: Good for shops or small fleets; pair with a DEF-rated pump and closed dispensing system.
• Bulk totes (e.g., ~330 gallons): Suited for high-volume users; often used with transfer systems and 12V pumps.

Consider pump/nozzle compatibility (look for DEF-rated components), flow rate needs, and connection sizes (such as 3/4-inch barbs). Buying the size you’ll use within a reasonable timeframe can help maintain product quality.

Crystallization can happen when DEF dries on surfaces or when contaminants enter the system. A few habits can help keep things running smoothly.

• Keep containers sealed and dispense with DEF-specific pumps and nozzles to avoid contamination.
• Wipe up spills promptly and cap the container and fill port securely.
• Avoid mixing non-DEF additives unless they’re specifically labeled for DEF/SCR systems and permitted by your vehicle manufacturer.
• Some DEF system cleaners and treatments are formulated to address deposits; effectiveness can vary, so follow label directions.

If you’re seeing repeated warnings or dosing faults, consulting a qualified technician and your owner’s manual can help identify the root cause.