The ins and outs of exhaust fluid
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Correct use important to avoid damage to your vehicle
What is diesel exhaust fluid?
More diesel-powered vehicles require diesel exhaust fluid (DEF) -- otherwise known as, Z DEC, AlliedBLue, GoClear, or AdBLue -- but what exactly is it?
DEF is a solution that's made with 32.5 per cent liquid urea and 67.5 per cent deionised water.
It's used as a consumable in selective catalytic reduction (SCR) in order to lower the concentration of harmful pollutants in the diesel exhaust emissions.
In the US, the Environmental Protection Agency rules for diesel vehicle emissions are the most stringent in the world. The majority of 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 many truck engines for years.
Diesel engines with SCR systems 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 broken down into nitrogen and water, which are released through the exhaust.
Mercedes-Benz BlueTec, Volkswagen, Peugeot and Citroen BlueHDi, are just some examples of cars 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 damage to your vehicle. A cool, dry, and well-ventilated area out of direct sunlight makes a great storage environment for DEF. Though this fluid isn't toxic, it is corrosive to some metals such as carbon steel, aluminium, copper and zinc.
This means if this fluid is ever 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 conventional service station. Make sure you remove the correct cap for the DEF tank -- it's generally the blue cap on the vehicle, and usually clearly labelled. If you choose to fill up at a truck stop, make sure you don't get the DEF and the diesel fuel pumps mixed up. Some will have completely 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 ever 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 car and get the fluid drained and disposed of correctly. Any contaminated components will need to be flushed out, and they may even require replacement to avoid long-term corrosion.
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 really easy.
It's also important to note that DEF doesn't last forever. Generally it has a two-year lifespan from its production date.
Keeping on top of exhaust fluid levels is crucial because vehicles 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 cause your car to shut down completely.
Don't let your DEF run out or you could find yourself broken down at the roadside -- a situation everyone wants to avoid.