Diesel Exhaust Fluid (DEF)

What is DEF?

Diesel Exhaust Fluid (DEF) is a solution of high purity urea and de-ionized water. It is the operating fluid required in vehicles using Selective Catalytic Reduction (SCR) technology. Engineers developed the technology to meet the 2010 emission standards for reducing nitrogen oxide (NOx) exhaust emissions from diesel engines.

The fluid is contained in a designated DEF tank and it is sprayed into the exhaust system before the catalytic converter breaks down NOx into harmless nitrogen and water vapors.

DEF has a shelf life of 12 months if the required storage conditions are followed. However, DEF that has been stowed for a longer period may be usable if analyzed to confirm that it still meets the DEF specification. Storage facilities can be adapted to suit customer needs.

How Does DEF Work?

DEF works through a process called Selective Catalytic Reduction (SCR). In 2010, SCR was mandated in diesel engines as an environmental initiative. SCR uses a catalyst system containing ammonia to break down Nitric oxide (NOx) emissions. NOx gases are the leading cause of air pollution. SCR can break down those emissions once DEF gets sprayed into the exhaust stream.

SCR has been around for nearly half a century and it was first used in the power generation industry to reduce oxides of nitrogen from coal-fired power plants.

Answers to your DEF Questions

What is DEF and how should it be used?

DEF is a mixture of high purity urea (32.5%) and water (67.5%). It is used to chemically reduce the concentration of nitrogen oxide (NOx) in the exhaust emissions from diesel engines. DEF is contained in a designated DEF tank on the vehicle. Never fill the diesel fuel tank with DEF or try to use it as a fuel additive.

How much DEF is required?

DEF does not have to be replenished every time the diesel fuel tank is being filled.

The required amount is about 3% of the vehicle’s diesel fuel consumption, i.e. For every 100 gallons of diesel fuel consumed, only 3 gallons of DEF is required.

Is DEF harmful?

DEF is non-toxic, stable, odourless and colourless. If it gets on your skin or clothes, rinse with water. If in eyes, flush with clean water for at least 15 minutes. Although DEF is colourless, avoid spilling on clothing or vehicle upholstery.

What makes DEF API Certified?

Heavy-duty vehicle manufacturers demand a high level of purity for DEF to honour the warranty they give on their vehicles. DEF is a quality fluid that is API certified and meets ISO 22241 to ensure its purity and composition. It is delivered in dedicated, sealed DEF containers for protection from contamination, to help prevent damage to the vehicle’s catalyst.

How should DEF be stored?

DEF should be stored in a cool, dry, well-ventilated area at a constant temperature. For optimal shelf life (12 months), store between 86°F/30°C and 12°F/-11°C. It is better to keep DEF indoors, but an outdoor heated enclosure/container is also suitable. Avoid storing in direct sunlight. DEF will freeze at 12°F/-11°C. However, frozen fluid can be thawed and used without concerns of product degradation.

How Often Does DEF Have to Be Refilled?

For typical trucks and SUVs, a tank of DEF needs to be refilled about as often as changing your oil. For semi-trucks, refill is required a lot more frequently due to the mileage on your truck.

How Much DEF Will My Vehicle Consume?

DEF consumption is usually measured in terms of the amount of “dose rate” of diesel your vehicle consumes. Therefore, if you are driving a long distance or use your vehicle often, you will use much more DEF than someone who works locally. Usually, they say that DEF tanks are to be refilled every 4,000 to 10,000 km, but that depends on the size of the vehicle and its use.

Does DEF Freeze During Cold Weather?

DEF freezes at -11 degrees Celsius, which is bound to happen in our Canadian winters! Typically, DEF thaws on its own from the heat of the engine and does not impact the functioning of the vehicle. Upon starting the vehicle, the SCR system provides heat to DEF tank, where it begins to thaw. As with any water-based fluid, DEF expands when it is frozen. Before shutting down the vehicle, wait a minute prior to turning off the battery. This delay will allow the fluid to drain out of the hoses and into the DEF tank.

How Will I Know if I’m Low On DEF?

Similar to when you are low on gas, you’ll know when you are low on DEF. All engines designed with SCR also come equipped with a gauge to display the DEF fuel levels. If you run out of DEF, lights will flash to notify you. Unlike gas, if you run out of DEF, it won’t impact the functioning of your vehicle.

What Are the Benefits Of DEF?

  • Reduced pollution- The main reason selective catalytic reduction was introduced was to help the environment. Diesel has been known to emit poisonous NOx emissions, typically blamed for causing acid rain and the greenhouse effect. With DEF turning the emissions into nitrogen and water, this is much more environmentally friendly.
  • Reduced maintenance- Engines designed with SCR technology have less wear and tear on their vehicles than those without, reducing the need for maintenance. Reduced maintenance also means that your vehicle is less likely to break down.

At Roma Fuels Ltd, we have been a family owned and operated business since 1968, fueled by exemplary customer service. We now offer DEF in the following formats:

  • Jugs (9.4L)
  • Drums (202L)
  • Bulk (1200L totes); or
  • Direct to equipment (wheel to wheel).

SCR Technology

Selective Catalytic Reduction (SCR) is a new technology which leading North American heavy-duty diesel engine makers adopted after testing various technologies intended for reducing emission levels to the required EPA standards.

SCR technology achieves the reduction of exhaust fume emissions required and allows for maximum engine operation in terms of performance and fuel economy.

The use of DEF API is the most effective way to take full advantage of SCR technology and to protect engine systems from the possibility of gradual degradation or clogging due to contamination. It also helps to prevent the loss of efficiency, costly parts replacement and engine downtime.

Other larger tank options are also available for customized solutions.


DEF are available in these sizes


DEF 5X6 Heated Hut
DEF 7X10 Heated Hut