Hydraulic System Fault — High Oil Temperature

What This Fault Means

A high oil temperature alarm indicates the hydraulic fluid has exceeded the safe operating range (typically 60°C / 140°F). Hot oil degrades seals, reduces viscosity, and accelerates wear on pumps and valves.

Common Causes

• Clogged or undersized heat exchanger (oil cooler)
• Low reservoir fluid level reducing heat dissipation
• Relief valve cracked or set too low, causing constant bypass heating
• Pump running at excessive pressure with internal leakage
• Wrong oil viscosity grade for the operating conditions

Recommended Fix

1. Check the oil cooler — clean fins, verify coolant flow (water or air), and confirm fan/pump operation.
2. Verify reservoir oil level is at or above the minimum mark.
3. Check the main relief valve setting against the circuit design pressure.
4. Look for excessive internal leakage by checking pump case drain flow (should be <5% of pump output).
5. Verify the oil viscosity grade matches the manufacturer's spec for ambient conditions.