Diesel genset wet stacking, load banking, and shutdown symptoms

Wet stacking is what happens when a diesel genset runs long periods at low load (below 30 percent of rating). Unburned fuel and moisture accumulate in the exhaust manifold, cylinder walls glaze, injectors carbon up, and rings lose tension. Symptoms: exhaust darkens from clear-to-light-gray to smoky black, oil consumption climbs, power output drops, exhaust manifold shows wet fuel weeping from the flanges. Prevention: run the genset at 40 to 60 percent of rated load for at least 30 minutes weekly. On a 20 kW genset that means 8 to 12 kW of real load, house AC plus water heater plus battery charger usually gets you there. If your normal load profile can't reach 30 percent, install a load bank (Simmark, Load Rite, or a DIY resistor bank) plumbed to a dump load like a water heater or a resistive heater on deck. Recovery from wet stacking: if caught early, run under 60 percent load for 4 hours consecutive, most units recover. If cylinder glazing is advanced (blue smoke persists, compression is low), only a top-end teardown will fix it. Never solve wet stacking by ignoring it; the injector damage cascades into fuel-system problems.