Fault Phenomenon: SANY SY215 excavator requires frequent coolant top-up, but no obvious external leak is found.

Troubleshooting Process:
– Checked head gasket: gasket blown, water entering cylinder or oil passage.
– Checked radiator cap: pressure valve failed, causing boiling overflow.
– Checked heater core: cab heater core internal leak.
– Checked water pump: pump seal micro-leak evaporating.

Root Cause: The engine cylinder head gasket is blown, allowing coolant to enter the combustion chamber and exit through the exhaust, or enter the oil system.

Required Parts: Engine cylinder head gasket assembly and coolant replacement.