SCR FAQs

By Brad Stemper | February 22, 2013

Q: What happens if the DEF tank is running low?

A: Some machines will warn the operator prior to the tank becoming empty (similar to the low diesel fuel tank warning). If the tank becomes empty, a de-rate/limp-home mode will eventually initiate, although the machine should provide approximately two hours of audible and visual warnings to the operator.

Q: How is the machine’s DEF tank heated?

A: The engine coolant runs through a heating element and warms the fluid inside the DEF tank. The DEF tank is designed not to be affected by freezing temperatures. Tier 4 regulations establish that the SCR system has 30 minutes to start functioning after engine startup.

Q: How will mud and debris buildup affect the SCR system?

A: Debris buildup has no effect on the SCR system. These have been designed to be suitable for all construction (and agricultural) applications and environments.

Q: How will operating on extreme side hills affect the SCR system?

A: There should be no effect. The SCR system functions on a grade just as the fuel system does.

Q: How does exhaust noise level vary from Tier 3 machines?

A: There is no significant difference with SCR machines.

Q: What percent of biodiesel can be used? Does biodiesel have any effect on the SCR system?

A: B5, B7 and B20 are approved blends, but it is important to know that blends over B5 may cause loss of engine power and shorten engine oil filter and fuel filter service intervals. Use only appropriate biodiesel blends that meet EN14212 or ASTM D6751 specifications. Biodiesel blends that do not meet certification can cause damage to the engine, fuel system and aftertreatment system.

Q: Are there filters that need to be changed, and how often?

A: There are two filters in the DEF circuit, which have a maintenance schedule equal to engine oil. One filter is in the DEF supply module.

Q: What happens if I accidentally put DEF in the diesel tank?

A: The severity of concern depends on the quantity of DEF in the fuel tank. Larger amounts will adversely affect fuel-system components. DEF will act similarly to water in degrading the fuel. 

Q: What happens if I accidentally put diesel in my DEF tank?

A: Small quantities of fuel in the DEF tank will most likely not be recognized. Larger quantities could result in damage to the catalyst chamber. To be safe, you should drain and refuel the DEF tank.

Q: DEF freezes; how is this addressed for winter storage on equipment?

A: On engine shutdown, DEF lines on the machine are emptied. The DEF tank is designed with an expansion allowance to accommodate if the DEF freezes.

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