If the surface is corroded or if the blades are damaged, replace the impeller

Water Pump Impeller Disassembly/Assembly
Water Pump Housing DisassemblyIdle Speed Control Valve Actuator Installation
Replace the O-ring [A] with a new one.
Apply engine oil to the new O-ring.
Install the idle speed control valve [A] as shown in the
figure.
10° [B]
Tighten:
Torque - Idle Speed Control Valve Actuator Retainer
Screws: 2.06 N·m (0.21 kgf·m, 18 in·lb)
Install th ...
Drive Chain Wear Inspection
Remove the chain cover (see Drive Chain Removal/Installation
in the Final Drive chapter).
Rotate the rear wheel to inspect the drive chain for damaged
rollers, and loose pins and links
If there is any irregularity, replace the drive chain.
Lubricate the drive chain if it appears dry.
...
Water Temperature Sensor Resistance Inspection
Refer to the Water Temperature Sensor Inspection in the
Electrical System chapter.
If the reading is within the standard, but the problem still
exists, replace the ECU (see ECU Removal/Installation in
the Fuel System (DFI) chapter).
Water Temperature Sensor Circuit
1. ECU
2. Water T ...