A Complete Guide to Choosing Your Diesel Exhaust Fluid

The market for diesel engines was worth more than $212 billion in 2021. Diesel engines built in the last decade need more than just diesel fuel to run. They also need diesel exhaust fluid.

Are you using the right diesel exhaust fluid?

Find out how to choose the best diesel exhaust fluid and get the most from what you buy.

What Is Diesel Exhaust Fluid?

Diesel exhaust fluid (DEF) is part of the selective catalytic reduction system in your diesel engine. Selective catalytic reduction (SCR) technology is part of the engine’s emissions control system. Manufacturers started using SCR systems to meet new EPA emissions standards in 2010.

The SCR system uses DEF to reduce tailpipe emissions of nitrogen oxides. DEF is made from 67.5% de-ionized water and 32.5% urea. Urea, also called carbamide, is a natural substance found in mammal urine.

How Does DEF Reduce Diesel Engine Emissions?

The SCR system injects DEF into the hot stream of exhaust gas. When DEF contacts the hot gas, the water boils and releases the urea. The urea breaks down into carbon dioxide and ammonia.

Ammonia strips the oxygen from the nitrogen oxides. The oxygen binds with the carbon dioxide to create water. After this process, the diesel engine emits almost nothing except water and carbon dioxide.

How to Find the Right Type of Diesel Exhaust Fluid

Many exhaust fluid brands are available. The most important criterion when choosing one is quality. DEF must meet high purity standards for the selective catalytic reduction system to work properly.

Purity and Quality Standards

Diesel exhaust fluid should meet the ISO 22241-1:2019 purity standard. The International Organization for Standardization (ISO) created and maintains this standard.

DEF should also meet EPA standards. EPA regulations limit the level of impurities that can be present in the fluid. The EPA specifies that DEF manufacturers must use pharmaceutical urea instead of agricultural urea because it’s purer.

Certification from the American Petroleum Institute (API) is additional quality assurance. The API certification program for DEF is voluntary. Fluids with API certification undergo monitoring and testing to ensure they follow the ISO 22241 standard.

Beware of Low-Quality Products

Higher-quality DEF will meet ISO 22241 requirements. It will have impurity levels well below the EPA limit.

Lower-quality DEF may not be DEF at all. Cheap products may say they’re “DEF compatible.” If they don’t follow ISO 22241, they’re not technically DEF.

Lower-quality DEF often has levels of impurities that are just below or equal to the EPA limit. These types of products work poorly and may even damage your engine.

Where to Buy DEF

Diesel exhaust fluid is widely available from auto parts stores, gas stations, and truck stops. You can also have DEF delivered to your fleet or equipment.

DEF delivery is a more economical option than paying retail prices. Regular deliveries save you from the hassle of managing your DEF inventory and placing orders. You avoid running out of exhaust fluid.

You can get your diesel fuel and DEF from the same supplier.

An internet search will help you find where to get DEF delivery to your location. Look for a supplier with a good reputation and certified products.

The supplier should be able to give you a certificate of analysis with every delivery. The certificate will show if the exhaust fluid meets the quality requirements.

How Much DEF Will I Need?

Your diesel engine uses much less diesel exhaust fluid than diesel fuel. DEF consumption is typically 2% to 4% of fuel consumption. For every 100 gallons of diesel fuel, you’ll use 2 to 4 gallons of DEF.

Some engines may use up to 10% relative to fuel consumption. Your usage can vary depending on factors like:

  • Engine manufacturer
  • Size of truck or machine
  • Engine type and transmission configuration
  • Workload

The DEF tank is often sized to be refilled with each fuel refill or every other fuel refill.

Unlike other diesel fluids, no additives exist to make DEF last longer. Any additive would contaminate the exhaust fluid. Contaminated fluid can cause severe engine damage.

How to Handle and Store Diesel Exhaust Fluid

Diesel exhaust fluid is non-toxic. It’s not flammable or explosive. However, it’s very sensitive to high temperatures and contamination.

Proper handling and storage are important to avoid possible engine damage from contaminated fluid.

Also, remember that DEF isn’t a fuel additive. It goes into a separate tank. Adding DEF directly to the fuel will ruin both fluids and could damage the engine.

Use the Right Storage Container

You should store DEF in a container made from one of these materials:

  • Titanium
  • Stainless steel
  • Rubber
  • Plastic

DEF reacts with many other materials like copper and aluminum. Its corrosive effects on these types of containers can contaminate the fluid.

The container you use for DEF should be new and dedicated exclusively to exhaust fluid. Any residue will cause contamination.

Avoid High Storage Temperatures

Heat shortens the shelf life of DEF. With proper storage, DEF can last a year or more.

Avoid storing DEF above 70ºF. Avoid outdoor storage locations because UV rays will damage the fluid. DEF can freeze and thaw with no problems, though.

Cleanup and Disposal

Small spills aren’t a cause for alarm because DEF is non-toxic and relatively clean. You can use sand or another absorbent material to soak up the fluid. Then you can dispose of the sand using your standard disposal service.

If DEF spills on the skin, wash it off right away with water.

Avoid sending DEF down drains or into water supplies because it could corrode the pipes. For disposal of large quantities of DEF, contact your local environmental agency.

Use the Right Diesel Exhaust Fluid

Diesel exhaust fluid is important for protecting the environment. Proper usage keeps you in compliance with the law. Choosing high-quality DEF from a reliable supplier is the key to protecting your engine and getting the best performance.

Keep reading for more helpful guides like this!