FAQs about Diesel Exhaust Fluid (DEF)

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• How does EGR work and why is this technology essentially being replaced by SCR?

  EGR stands for Exhaust Gas Recirculation. EGR was the technology that most manufacturers used to meet the first rounds of emissions regulations in 2004 and 2007. In an EGR system, exhaust gas is cooled and recycled back through the engine. The combustion temperature in the cylinder is reduced, thus lowering NOx production. However, the cooler combustion produces more particulate matter due to the less efficient operating temperature. Also, the engine is not operating at its optimal combustion temperature, consequently reducing fuel efficiency and engine power.The advantages of an SCR system is that it allows the engine to operate at higher temperatures in order to optimize performance, meanwhile reducing NOx levels.

• What are the disadvantages of SCR?

  The disadvantages of SCR are mainly logistical. SCR requires the addition of DEF (Diesel Exhaust Fluid) to the system as needed; consumption rates are dictated by engine usage. The distribution system for DEF is still in its infancy and, although DEF is available at many locations throughout the country, operators in remote locations may find it more difficult to acquire. Bodybuilders and Upfitters may have challenges working around the packaging of the new SCR systems as they take up more real estate on the chassis.

• What maintenance is required of an SCR system?

  The SCR system maintenance is relatively easy and conducted at the same intervals as normal chassis maintenance. DEF filter changes only take a few minutes and replacement cycles will most likely be measured in years rather than months.

• What happens if my vehicle runs out of DEF?

  The answer to this question will vary based on manufacturer and year of your vehicle. Most manufactures have added new instrument gauges and indicators to vehicle dashboards or on-board displays. There will be a progressive series of warning and indications coupled with performance reductions in the vehicle if the SCR is allowed to operate without DEF. Please consult your OEM website for more info (a list of OEM links is available on this site).

• What happens to DEF if it exposed to high temperatures?

  DEF’s shelf life begins to degrade at high temperatures. If it is maintained at or above 120 degrees Fahrenheit it will slowly begin to form small amounts of ammonia. Check with your supplier of DEF to for more information on proper handling of DEF in extreme temperatures.

• What is DEF?

  DEF stands for Diesel Exhaust Fluid. It is a 32.5% solution of chemically pure Urea and 67.5% demineralized or deionized water. It is a non-regulated non hazardous solution. You may also see it referred to as NOx reduction agent AUS32 or AdBlue, both terms are common in Europe.

• What is DEF used for?

  Most diesel engine manufacturers have adopted SCR (Selective Catalytic Reduction) technology to meet 2010 EPA emissions standards. “SCR is the aftertreatment technology that treats exhaust gas downstream of the engine. Small quantities of DEF are injected into the exhaust upstream of a catalyst, then converts to ammonia in the exhaust stream and reacts with NOx over the catalyst to form harmless nitrogen gas and water.” Source: www.cumminsfiltration.com.

• Is DEF a fuel additive?

  No, DEF is injected into the diesel engine’s exhaust stream. It is stored in its on stand-alone tank, usually located right beside the diesel tank. It commonly has a blue cap or other blue indicator to identify it as DEF (whereas diesel is often associated with the color green).

• Is DEF a hazardous substance?

  No, DEF is a stable, non-toxic solution that can be transported without the use of a DOT approved hazardous substance placard.

• What does DEF look like?

  DEF is a clear, colorless liquid.

• How much does DEF weigh?

  DEF weighs approximately 9 lbs per gallon. Compared to diesel fuel at approx 7.05 lbs and gasoline at an average of 6.19 lbs, DEF is a relatively heavy product.

• Does DEF go bad?

  As long as DEF is stored between 10 and 90 degrees Fahrenheit it should last at minimum of 1 year.

• Does DEF freeze?

  Yes, DEF has a freezing point of +12 degrees Fahrenheit but the DEF can be used after it thaws from its frozen state.

• I keep hearing about how important DEF purity is. How do I know if my DEF is pure and up to spec?

  The only true way to know would be to pull a sample and send it off to a laboratory for testing. However, many manufacturers have become API (American Petroleum Institute) certified, a voluntary program that monitors the quality of DEF. Remember, DEF is a clear, colorless liquid. If you see any color, haze, phase separation, or sediment in your DEF container, this should be an immediate red flag.

• Is SCR new technology?

  SCR has been used in Europe since 2006 and has a proven track record. There are more than 600,000 SCR trucks operating in Europe with more entering the market each day.

• Can I use agricultural grade UREA in my SCR vehicle?

  No, DEF is a very pure solution of high grade Urea and demineralized or deionized water. Agricultural grade Urea often has additives such as formaldehyde to prevent the product from clumping when in a dry form.

• Is DEF and SCR just for cars and trucks?

  No, In order to meet EPA emissions requirements in 2013 and 2014 and beyond, off-road diesel engine manufacturers are beginning to adopt this same technology early. This is leading to use in locomotives, tractors mining and boats and seagoing vessels.

• What are the benefits of SCR technology?

  Besides the obvious environmental benefits, SCR technology has been reported to increase fuel efficiency by anywhere from 4% to 9% by allowing diesel engines to operate at more efficient temperatures.

• What is Urea?

  Urea is a compound of nitrogen that turns to ammonia when heated. It is commonly used in agriculture as fertilizer.

• Will DEF harm my aluminum tank?

  Although DEF will not “harm” many materials, it is actually the metal of many storage containers (such as aluminum) that will leach into the DEF and contaminate it.

• What materials are compatible with DEF?

  There are far more materials that are not compatible with DEF than are. Stainless steel and DEF approved poly are commonly used materials in the construction of DEF equipment. ISO 22241 defines what are acceptable materials for use in the storage and handling of DEF. Specially formulated DEF hose must be used in the transfer and dispensing of the Diesel Exhaust Fluid.

• Does DEF have an MSDS sheet? If so, where can I obtain this document?

  Yes, Contact your supplier of DEF for an MSDS sheet.

• How much will DEF cost?

  DEF is typically priced by the gallon and prices in this emerging market have fluctuated wildly. Packaged goods (shelf goods) are usually priced higher per gallon than bulk (from dispensers) because the consumer is also paying for the packaging along with the product. In Europe, where the market has had time to mature and distribution is more established, DEF averages between $2 and$5 per gallon.

• Where can I get DEF?

  Although the distribution of DEF in the US is an emerging industry, most major truck stops, gas stations, and auto/truck dealerships will carry the product in packaged form. Some of these same establishments will also offer DEF fill-up and top-off through dispensers. Many of the users of DEF will also be installing small bulk dispense systems at their facilities. For a list of locations check out the website www.discoverdef.com.

• How much DEF will my SCR vehicle consume?

  Initial estimates range from 2% to 3% consumption rate. For example, for every 100 gallons of diesel fuel burned, approximately 2 to 3 gallons of DEF will be used. However, results will vary by engine make and model and off-road vehicles may consume DEF at a greater rate with a larger fuel efficiency gain as well.

• How big will the DEF tank be on my vehicle and what will it be made of?

  We have seen tanks beginning at 4 gallon capacity going up to 28 gallons for on-road vehicles. Size and position will vary by manufacturer and model. Larger tanks will be need for bigger off-road vehicles that consume more fuel. DEF tanks are made of DEF approved poly or stainless steel.

• If I need to dispose of DEF that is off-spec, what is the best practice for doing so?

  Although DEF is not a hazardous material, check with your local government, municipal, and environmental agencies on the proper method of disposal. These entities will include (but are not limited to) your local water treatment facility and department of health and environmental control. Also, check with your DEF supplier for more instructions.

• I see white, chalky residue around DEF equipment and containers. Is this normal?

  Yes, as the liquid evaporates out of the DEF solution the urea returns to its solid, concentrated state. (Think about salt water that is left to evaporate and leaves the salt residue behind.) A simple wash with deionized water will remove sediment and any built up deposits. Nozzles are common places to see this residue.

• How is DEF delivered and packaged?

  DEF can be delivered in a variety of packages or bulk dispensing systems. The smallest of these are packaged goods, or what are commonly referred to as “jugs”. The most common size packaged goods are 1 and 2.5 gallons and are stocked at most truckstops and dealerships throughout the country. The next step up is 55 gallon drums which may or may not be refilled. Hand pumps and electric drum pumps may be fitted to the top of the drums for dispensing the product at about 4-8 gpm. Totes are used for storing and transporting DEF in 275 gal or 330 gal capacities. Pumps are available that mount on top or to the side of the tote for dispensing. Tote pumps often include a digital flow meter.

• How much DEF can I haul?

  With DEF weighing in at around 9lbs per gallon, we estimate that with a tandem axle truck tank you will be able to haul just over 3000 gallons in most states. For trailers the capacity will be around 5,000 gallons. However, Oilmen’s Truck Tanks uses sophisticated weight distribution software on all the units we build. Give us a call and we can give you a more definitive answer to the question based on the specifications of your vehicle.

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