Fault Phenomenon: Putzmeister M52 oil temperature rises normally when cold. After reaching operating temperature (oil temp 85℃), the oil temperature rises too quickly, the system enters protection mode, and pumping is weak.

Troubleshooting Process:
– Checked radiator exterior: no debris, fan airflow normal.
– Checked hydraulic oil viscosity: oil grade correct, not deteriorated.
– Checked thermal bypass valve: opening pressure normal when cold.
– Measured bypass valve opening pressure at operating temperature: found valve opens prematurely.

Root Cause: Spring fatigue in the hydraulic oil cooler bypass valve prevents it from closing under thermal conditions.

Required Parts: Hydraulic oil cooler bypass valve assembly.