The Environmental Protection Agency’s recent finalization of their Clean Trucks Plan brings the biggest changes to heavy-truck emissions standards in decades.

But not everything will change. Fleets and truckers can expect diesel exhaust fluid (DEF) to continue to play an essential role in reducing harmful pollutants out on the road. DEF is the liquid that makes today’s leading-edge exhaust control technology, or selective catalytic reduction (SCR) systems, go. And it’s not going anywhere.

Here are ten things that fleets and truckers need to know about diesel exhaust fluid to reap its full environmental, efficiency and economic benefits—and feel good about doing it

1 - DEF Helps Reduce Harmful Emissions to Near Zero

When used in diesel engines with SCR systems, DEF reduces the release of nitrogen oxides (NOx) by up to 90%.  

NOx is a dangerous pollutant created when diesel is burned at high temperatures. It is a key target of emissions control because it can cause respiratory problems and heart disease. Furthermore, when it is released into the atmosphere, NOx contributes to climate change, smog and acid rain.  

The threat posed by NOx to individual health and the environment at large led the Environmental Protection Agency (EPA) to mandate SCR that uses DEF in most diesel-powered trucks and cars built since 2010.  

2 - Diesel Exhaust Fluid Is a Simple, Safe Additive

When DEF is added to the SCR system of a diesel engine, the fluid reacts with the harmful nitrogen oxide (NOx) gasses created during combustion. As a result, NOx gas is converted to non-toxic nitrogen, water and minimal amounts of carbon dioxide (the same stuff humans exhale).

Not only are the byproducts of DEF harmless, DEF itself is considered one of the safest compounds in the shop. It is composed of 67.5% deionized water and 32.5% urea (a compound found in urine).

3 - It's Effective in Safeguarding the Environment

Converting nearly all NOx from trucks’ exhaust is a significant feat. The net effect of DEF use adds up when applied to trucks across the country. 

According to the Environmental Defense Fund, delivery trucks and tractor trailers are responsible for nearly half of the NOx emissions from vehicles on U.S. roads. 

As an integral ingredient of SCR, DEF helps make diesel engines safer for the environment than ever by reducing NOx as well as particulate matter, carbon monoxide and hydrocarbons—all of which cause respiratory problems, impact air quality and contribute to the creation of smog.

4 - DEF Use Can Improve Vehicle Performance

The environmental and public health upsides of using DEF come with no downsides for truck performance. In fact, DEF can improve fuel efficiency and extend engine life. 

According to the Maryland Department of the Environment, heavy-duty engines that use DEF-reliant SCR technology receive a fuel economy improvement of up to 5%. Considering today’s high diesel prices, those savings can add up.  

DEF also plays an essential role in optimizing emissions control for peak engine performance. As a result, DEF usage can increase horsepower, reduce engine wear and decrease the frequency of diesel particulate filter changes.

5 - Modern Emissions Control Technology Relies on DEF

SCR is the predominant technology used by engine manufacturers to comply with EPA standards regarding emissions. DEF is so important to SCR systems that without it, they won’t work. That’s why it’s important to know how DEF and SCR work.  

In engines using SCR technology, DEF from a tank stored on the truck gets injected into the exhaust system after the diesel has burned. The DEF reacts with the exhaust gases and converts the toxic NOx into non-toxic nitrogen and water vapor.

 6 - Take Care to Monitor and Maintain DEF Systems

DEF systems have sensors to monitor the DEF level and the integrity of the fluid in a truck’s DEF tank. Systems need to be tested and calibrated on a regular basis to maintain accuracy—they also need to be heeded when warning lights go on. Warnings caused by low DEF levels, dirty filters or sensor failures can signal problems that, left unattended, can compromise engine performance and allow harmful emissions to escape.  

Pay careful attention to warning lights indicating fluid levels are low. If you ignore the warnings, trucks tend to go into low power mode and limit maximum speed. If you continue to drive with low DEF levels, maximum speed will continue to fall and eventually the truck will stop.

Lots of drivers top off DEF levels every time they stop for diesel to avoid this unpleasantry.

7 - DEF Is Easy to Buy (If You Know Where to Look)

DEF is a standard, unvarying compound, always made of 32.5% urea and 67.5% deionized water. There are no product variations to weigh when you buy it. DEF prices and quantities are the only considerations. Quantities go from 32 ounces to 330 gallons and prices can vary widely. 

Because trucks can go through a fair amount of the compound, it is advantageous for shops to have a trusted supplier who maintains your DEF stock.  

The reality is that truckers need DEF when they need it. That’s often out on the road where truck stops are the best bet.  

DEF is diesel-specific and is not sold everywhere or at every gas station. For this reason, Imperial Supplies recommends keeping an emergency jug of DEF in trucks to avoid running out.

8 - Make Sure Your Product Comes From a Trusted Source

DEF must meet precise standards and DEF production is strictly regulated to ensure chemical purity. Major engine manufacturers require the DEF used in their SCR systems meet ISO 22241 standards and the certification guidelines of the American Petroleum Institute (API).  

Beware of products that don’t bear both these insignias. Major brands of DEF all meet these requirements and their labels will say so.  

In addition to looking for these two requirements on the label of DEF products, look for the original production date. Make sure it is within two years of when you are buying it.

9 - Care and Handling of DEF Matters

DEF will last for two years if properly stored; however, the wrong conditions can compromise its quality and shorten that shelf life. If the container is leaking or open to dust and debris, the purity of the DEF will be in question and using it can harm systems.  

Additionally, DEF should be stored at ambient temperatures of 75 F. Long-term heating to temperatures over 86 F or exposure to direct sunlight can degrade DEF faster and shorten its useable life. This is a potential drawback of keeping spare DEF in trucks for prolonged periods. 

As for handling, DEF is safe to touch, no protective clothing required. It’s also easy to clean when spilled. You can simply wipe it up or leave it to dry. Nevertheless, DEF is corrosive to certain metals. So be sure not to store it in containers made of aluminum, carbon steel, copper or zinc.

10 - Know Your DEF Consumption Rate and Plan

Avoid running out of DEF and take advantage of bulk discounts by estimating your DEF consumption. Imperial Supplies helps its customers calculate the amount of DEF they need, and help schedule a plan for delivery and storage.

According to Cummins, a leading manufacturer of heavy-duty engines, DEF consumption is 3% to 5% of fuel consumption. Their website says that as fuel consumption increases, so too does DEF consumption. Therefore, when estimating DEF needs, they advise using the highest fuel consumption rate in calculations.  

Imperial Supplies Makes DEF Super Easy 

DEF and its proper use in SCR systems is critical to complying with emissions regulations, protecting the environment and ensuring the optimal performance of your equipment.  

Talk to a team member about your product options and how you can set up an auto reorder program that ensures a reliable, cost-effective flow of DEF for your vehicles. Imperial Supplies is an expert in fleet maintenance with 65 years of experience helping shops maintain the products they need to keep their shops and trucks operating at full capacity.