A granite quarry reported that a XCMG LW500K wheel loader would overheat (transmission temp > 130°C) after just one hour of loading trucks. The machine also felt "sluggish" when climbing the ramp to the crusher, as if the engine power was not being transmitted to the wheels.
The technician first checked the transmission oil. It was full but had a "milky" foam appearance, indicating aeration. He checked the "Transmission Oil Cooler" located near the hydraulic tank. The cooler fins were heavily coated in stone dust, blocking airflow. He pressure-washed the cooler, clearing the external blockage. However, the temperature still rose quickly.
He then focused on the "Torque Converter." He connected pressure gauges to the torque converter inlet and outlet. The inlet pressure was low (0.3 MPa vs. spec 0.5 MPa), and the outlet pressure was erratic. He removed the torque converter housing. He found the "Pump Impeller Seal" (the input shaft seal) was leaking. This leak was allowing air to be sucked into the oil stream.
The air bubbles (aeration) caused two problems: First, the air compresses inside the torque converter, reducing the fluid coupling efficiency, which explained the "sluggish" performance and torque loss. Second, the air caused the oil to foam. Foam has very poor heat transfer properties. The oil could not absorb heat from the torque converter efficiently, leading to the rapid temperature rise.
The repair involved replacing the torque converter seal kit. The transmission oil filter and suction hose were also replaced to ensure no debris remained. After refilling with fresh 8# hydraulic transmission oil and bleeding the system, the torque converter pressure stabilized, and the temperature remained at a normal 85°C under load.
