Tier 4 Final engines run incredibly clean, but they still produce soot. To clean the Diesel Particulate Filter (DPF), the ECU initiates an "Active Regeneration." It injects raw diesel fuel into the exhaust stream via a seventh injector (or in-cylinder post-injection) to raise the exhaust temperature to 1,100°F, burning the soot into ash. In a perfect world, this happens seamlessly. In the real world of cold-weather short-cycling, it is destroying engines from the inside out.
If a machine is idling in freezing weather, the exhaust never gets hot enough for a passive regen. The soot load builds, and the ECU forces an active regen. But because the engine is cold, the fuel sprayed during post-injection doesn't vaporize completely. Instead, it washes down the cylinder walls as liquid diesel.
This diesel seeps past the piston rings and dilutes the engine oil in the crankcase. Over hundreds of hours of short-cycling, the oil pan fills with diesel. Mechanics call this "making oil." The oil level on the dipstick actually rises. This diluted oil loses its viscosity and its ability to lubricate. Main bearings spin, turbochargers grenade, and cylinder walls scuff. The very system designed to save the environment is turning the engine's lifeblood into a combustible solvent. To prevent this, operators are forced to lock the machine at high idle for 30 minutes a day just to boil the diesel out of the oil and complete the regen cycle.
