Komatsu HM400-3 HM400-5 Radiator Fan Motor 708-7P-00020 708-7P-00030 708-7W-00230

Drives the cooling fan to dissipate heat from the engine and hydraulic system. Automatically reduces speed at idle or low temperature to save fuel and reduce noise, and increases speed under high temperature or heavy load to ensure adequate cooling.

• Fan not rotating / abnormal speed: First determine whether the fault is in the pump or motor—measure the fan motor inlet pressure/flow. If pressure is normal but the fan does not turn, it indicates internal motor wear; if pressure or flow is insufficient, check the fan pump, filter and oil circuit.
• Abnormal noise / squealing: Worn internal motor bearing, cavitation (air entrained in system), contaminated oil.
• Unstable fan speed / jitter: Abnormal electronic control signal, seized motor displacement mechanism, air in oil circuit.
• Oil leakage: Aged shaft oil seal, worn end-cover O-rings.
• High oil temperature chain reaction: Severe motor internal leakage generates heat, which in turn accelerates wear.

• Light wear: Replace the oil seal + seal kit and clean the interior.
• Severe scoring (cylinder block, valve plate, piston): Replace the rotating group parts or the complete motor assembly.
• Important: After reassembly, always fill the pump/motor with hydraulic oil before starting; running it dry will burn out the motor.