Fault Phenomenon: Volvo G990 grader shortly after operation, the hydraulic system overheats, and the machine automatically reduces speed.

Troubleshooting Process:
– Checked radiator: hydraulic oil cooler clogged.
– Checked fan: fan belt slipping.
– Checked relief valve: system in relief state for extended periods (improper operation).
– Checked oil: incorrect oil viscosity.

Root Cause: The operator habitually held the blade against an obstacle (relief condition), generating excessive heat, combined with reduced cooler efficiency, leading to overheating.

Required Parts: Clean radiator and correct operation procedure.