If the valve is open, replace the thermostat with a new one.

The thermostat must be completely submerged and must not touch the container sides or bottom. Suspend an accurate thermometer [B] in the water so that the heat sensitive portions [C] are located in almost the same depth.
It must not touch the container, either.
If the measurement is out of the specified range, replace the thermostat with a new one.
Thermostat Valve Opening Temperature
58
62°C (136
144°F)

Thermostat Installation
Hoses and PipesRadiator Hose and O-ring Replacement
Drain the coolant (see Coolant Change).
Remove:
Upper Fairing Assembly (see Upper Fairing Assembly
Removal in the Frame chapter)
Thermostat Housing [A] (see Thermostat Removal in the
Cooling System chapter)
Oil Cooler [B] (see Oil Cooler Removal in the Engine
Lubrication System chap ...
Swingarm Bearing Removal
Remove:
Swingarm (see Swingarm Removal)
Collar [A]
Oil Seals [B]
Sleeve [C]
Circlip [D] (Right Side)
Special Tool - Inside Circlip Pliers: 57001-143
Remove the ball bearing and needle bearings.
Special Tool - Oil Seal & Bearing Remover [A]: 57001-1058
...
Parts Location
1. Timing Rotor
2. Crankshaft Sensor
3. Horn
4. Oil Pressure Switch
5. Rear Brake Light Switch
6. Oxygen Sensor (Equipped Models)
7. Alternator
8. Stator Coil
9. Gear Position Switch
10. Sidestand Switch
11. Immobilizer Amplifier (Equipped Models)
12. Radiator Fan Motor
1 ...