Fault Phenomenon: LiuGong HBT100 cooling functions normally when cold. After prolonged operation (operating temperature), the coolant boils, the expansion tank overflows, and eventually the engine overheats.

Troubleshooting Process:
– Checked thermostat: opens normally, no sticking.
– Checked water pump impeller: impeller intact, no corrosion.
– Checked radiator: exterior clean, interior unobstructed.
– Measured cooling system pressure at operating temperature: found excessive system pressure.

Root Cause: The pressure valve spring in the radiator cap fatigues, causing it to open prematurely.

Required Parts: Radiator cap assembly.