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 PipesECU Removal
NOTICE
Never drop the ECU especially on a hard surface.
Such a shock to the ECU can damage it.
Remove the upper air cleaner housing (see Air Cleaner
Element Replacement in the Periodic Maintenance chapter).
Lift up the ECU [A] with rubber protector [B] to disconnect
the connectors [C]. ...
Engine Oil Flow Chart
1. Oil Screen
2. Oil Pump
3. Oil Pressure Relief Valve
4. Oil Filter
5. Oil Pipe
6. Oil Cooler
7. Balancer Oil Passage
8. Main Oil Passage
9. Crankshaft Oil Passage
10. Oil Pressure Switch
11. Camshaft Oil Passages
12. Drive Shaft Oil Passage
13. Output Shaft Oil Passage
14. Starter ...
Tire Installation
WARNINGSome replacement tires may adversely
affect handling
and cause an accident resulting in serious injury
or death. To ensure proper handling and stability,
use only the recommended standard tires for
replacement, inflated to the standard pressure.
Inspect the rim ...