Fault Phenomenon: Caterpillar 777 mining truck during continuous uphill operation, transmission oil temperature exceeds 125°C, machine automatically downshifts for protection.

Troubleshooting Process:
– Checked cooler: transmission oil cooler exterior clogged with mineral dust.
– Checked fan: fan clutch failed, speed insufficient.
– Checked oil level: low oil level causing insufficient circulation cooling.
– Checked clutches: internal transmission clutch slipping generating high heat.

Root Cause: The transmission oil cooler fins are completely clogged with fine mineral dust, and the fan silicone clutch failed, resulting in loss of cooling capacity.

Required Parts: Clean cooler, replace fan silicone clutch and transmission fluid.