Wet stacking is a problem with diesel engines and isn't limited to the Cummins engine or just because of DEF requirements. "Wet stacking" happens when a diesel engine is run too long with no load and operates below its optimum temperature. Unburned fuel can foul the fuel injectors, valves, turbochargers and more.
To overcome this problem during long idle periods, the engine must run at a fast idle, especially in cold weather, to keep the engine temperature up.
2015 Wildcat 282 RKX
2011 F350 Lariat, 6.7 L. Diesel, 8 ft., SRW, Reese R20