More diesel-powered vehicles these days require diesel exhaust fluid (DEF), which simply is an extra fluid that is injected into a diesel vehicle’s exhaust system to reduce emissions.
DEF fluid is branded as Z DEC, AlliedBlue, GoClear, or AdBlue and is a solution made with 32.5 per cent liquid urea and 67.5 per cent deionised water. It’s used as a consumable in a process called “selective catalytic reduction” (SCR) in order to lower the concentration of harmful pollutants in the diesel exhaust emissions.
In the United States, the Environmental Protection Agency’s (EPA) rules for diesel vehicle emissions are among the most stringent in the world. Most manufacturers have found the only way to comply with the EPA’s rules, without compromising engine performance and fuel efficiency, is through SCR, which has been common in truck engines for years.
Diesel engines with these systems fitted will have a separate tank for holding the DEF. The fluid is injected into the pipeline of the exhaust, causing a chemical reaction and it’s within the SCR system that the harmful pollutants are then broken down into nitrogen and water. Mercedes-Benz BlueTec, Volkswagen, Peugeot and Citroen BlueHDi, are examples of vehicles equipped with SCR systems.
If you have a vehicle that requires DEF, it’s important to store and use it correctly to avoid contamination and causing damage to your vehicle. A cool, dry, and well-ventilated area out of direct sunlight makes a great storage environment for DEF.
Although this fluid isn’t toxic, it is corrosive to some metals such as carbon steel, aluminium, copper and zinc. This means that if this fluid is poured into the fuel tank, it can cause serious damage to your vehicle.
Generally, the size of the DEF tank has been designed so owners don’t have to refill between service intervals, but if you do need to fill up on DEF, you can buy a small container of the fluid from a service station or vehicle manufacturer.
Make sure you remove the correct cap for the DEF tank — it’s generally the blue cap on the vehicle and it is usually clearly labelled.
If you choose to fill up at a truckstop, make sure that you don’t get the DEF and the diesel fuel pumps mixed up. Some will have separate dispensers for DEF and diesel fuel, making identification between the two easier.
However, be aware that some stations will dispense DEF at the same pumps as diesel, which can be confusing.
Always read the signage on fuel pumps carefully before filling up. And, if you’re unsure which pump to use, it’s better to stop and fill up at a regular service station.
If you make the mistake of putting DEF straight into the fuel tank, do not turn on the ignition or start the vehicle, and make sure the fluid is drained and disposed of correctly. Any contaminated components will need to be flushed out. in the worst-case scenario, the complete fuel system will require replacement.
On average, a litre of DEF should last about 1000km. However, usage can be higher depending on how and in what conditions the vehicle is driven. Some vehicles will have an alert system to warn the driver when the DEF tank level drops below a certain percentage, making maintenance easy. It’s also important to note that DEF doesn’t last forever and that generally it has a two-year lifespan from its production date.
Keeping on top of your exhaust fluid levels is crucial because vehicles equipped with an SCR system cannot operate without DEF.
Failing to keep your exhaust fluid levels topped up can compromise your vehicle’s fuel economy and can also cause your car to shut down. So, don’t let your DEF run out or you could find yourself broken down at the roadside — a situation everyone wants to avoid.