Ad Blue Usage – Helpful Information and Guidelines

Aug 9, 2019

What you need to know about Ad Blue (DEF).

This information is general to most makes and models of cars, buses, tractors and machinery that use Ad Blue.

Keep it clean.

Always use only quality Ad Blue fluid and keep it clean. Even trace amounts of a wrong fluid (like diesel or wiper fluid) can trigger a problem with the the system. This can put engines in a derated condition until corrected. To correct any mistakes, a full system clean is usually required. Keep dispensers and any funnels used clean and dedicated only to Ad Blue. DO NOT re use the containers if possible.


Ad Blue that remains in the tanks of machines sitting idle for an extended period will have a shorter shelf life. Fluid left in vehicles without replenishment and/or use may experience some water evaporation, changing the concentration of the fluid. This is also true for storage of opened Ad Blue tanks or barrels. General recommendations are to check Ad Blue fluid concentration using a refractometer after two or more months of storage.


Since Ad Blue is 2/3 water, the solution will freeze when the vehicle is not in use. This also occurs when temperatures approach -11°C. However, the system is designed to recover from a frozen tank. Coolant from the engine is circulated in a coil immersed in the Ad Blue tank to return the solution to liquid – generally within an hour after starting. During this thawing time, the vehicle can be utilized as it normally would be (as long as it is allowed to remain running). The Ad Blue pump will continue to run for approximately 45 seconds after the engine has been turned off to allow it to purge the lines of fluid. This is also to stop freezing. It is recommended that you do not turn of the battery isolators nowadays.

Keep at appropriate fill levels.

With most machinery, if the solution level in the tank is overfilled, or allowed to become too low for too long, the engine system will eventually derate itself until the vehicle becomes inoperable.


Some tanks have a filler neck screen. Remove and clean when debris appears. Ad Blue tanks have a suction screen where the fluid is drawn out of the tank to the pump – follow maintenance guidelines for replacement in the operator manual. The pump units also have a filter cartridge – follow maintenance guidelines for replacement in the operator manual. Finally, some systems also require a maintenance regeneration after an extended period of engine operation to remove any crystallisation that may have accumulated at the injector or within the exhaust system. Regeneration is generally an automated process where the machine carries out a cleaning cycle. During this period, the engine may automatically run at elevated speeds. This is to increase exhaust system temperatures to levels needed to clean the system – consult the machine operator manual.

Smart machine operation is important.

How you operate the machine will affect this system. As with any exhaust after-treatment system, adequate exhaust temperatures are required to keep the system operating optimally and efficiently. Avoid continuous low load and short interval start / stops of the engine that don’t allow the exhaust system temperature to stabilise. The machine needs to be regularly used in different modes to ensure engine loads and temperatures are reached to ensure the system is operating and cleaning correctly.


*The above information is taken from general guidelines. It should not replace the operator’s manual. Your operator’s manual will have guidelines specific to your machine.*

Jim Macadam Equipment sells Blue Cat and Optispray Ad Blue. Please contact our Parts department for more information.



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