What is Diesel Exhaust Fluid?

DEF (or alternatively Z DEC, AlliedBLue, GoClear, or AdBLue), is a component used in diesel powered engines designed to reduce harmful emissions. The fluid is made with 32.5% liquid urea and 67.5% deionised water and is used in selective catalytic reduction. 


SCR System

SCR is a system fitted into the engines of trucks  and is the most successful way to comply with rules surrounding diesel exhaust emissions. The biggest benefit to the SCR system is that it doesn’t compromise the engine and it’s fuel. DEF is held in a separate tank within the SCR system. DEF is transported into the exhaust via a pipeline for the SCR to then breakdown the harmful pollutants. Once the pollutants are successfully broken down into nitrogen and water the fluids can exit the exhaust. 

Engines fitted with an SCR system cannot operate without sufficient levels of DEF. Low exhaust fluid levels will cause your engine to shut down and thus cause your machine to break down. More often than not your diesel engine will hold the necessary DEF levels between. However, the shelf life of the fluid is only two years, so if you’re not using your vehicle/machine often, it’s easy to be caught out. If you are running low, it is likely your machine will notify you and you will be able to find DEF at most Petrol stations. Accidentally put DEF straight into your tank? You will need to have it flushed out or possibly replaced to reduce the risk of corrosion. 

If you choose to keep DEF at home, correct storage is essential especially considering the risk of corrosion. DEF isn’t a harmful substance however it can be corrosive to copper, aluminium, zinc and carbon steel. By keeping the fluid, cool, dry and well ventilated, you will decrease your chances of contamination which will inevitably affect your vehicle/machine. 


Here are some quick facts to remember

  1. DEF should only come into contact with stainless steel, titanium, rubber and plastic.
  2. You cannot repurpose any tank to hold your DEF. Pre Used tanks will most likely cause contamination in the DEF
  3. If your DEF has changed colour, the fluid has been compromised. 
  4. You cannot restore contaminated DEF. 
  5. Temperature can affect the shelf life of your DEF but unfreezing DEF will not.