A gravel quarry reported that a Shantui SL50W wheel loader was triggering the transmission overheat alarm (oil temperature > 120°C) after just two hours of continuous loading work. The machine had been serviced recently, including an oil change.
The technician first checked the external environment. The transmission oil cooler (located near the hydraulic tank) was covered in thick dust. He cleaned the cooler fins with a pressure washer, but the temperature still rose rapidly during stall tests.
He then connected a pressure gauge to the "Torque Converter Outlet" port. The pressure was low (0.2 MPa), indicating insufficient flow through the converter. The torque converter relies on a constant flow of oil to transfer power and remove heat. He suspected a restriction in the supply line.
He removed the "Transmission Filter" and found it was filled with a fine metallic paste. This indicated internal mechanical wear. He removed the torque converter housing cover. The "Stator Support" (which holds the fixed stator blade) was examined. The support bearings were severely worn, allowing the stator to wobble.
The worn stator bearings caused the stator to rub against the pump impeller and turbine runner, generating friction heat. Additionally, the wear debris had clogged the internal "Regulator Valve" in the transmission valve block. This valve controls the oil flow to the cooler. The debris prevented the valve from opening fully, restricting the cooling flow.
The repair involved replacing the torque converter assembly (due to stator support damage) and flushing the entire hydraulic system. The transmission valve block was disassembled and ultrasonically cleaned to remove the debris. After installing a new oil filter and refilling with fresh 8# hydraulic transmission oil, the system operated at a stable 85°C under full load.
