Wet stacking occurs in a diesel engine when the engine is run at too light of a load during the run-in (also known as load banking). This causes unburnt fuel and oil to collect in the exhaust stack. The exhaust stack will be coated with a black, sticky, tar-like substance. If you run a new unit at light loads and/or idle for too long, the rings will not seat properly. If it is a diesel, wet stacking may occur. Both of these conditions will cause poor engine life and performance.
This info is from
www.gendco.com
