Komatsu PC138USLC Operation & Maintenance Manual page 285

MAINTENANCE PROCEDURE MAINTENANCE PROCEDURE
13. Drain the water from sub tank (6), wash the inside of the sub
tank, then add cooling water to a point midway between the
FULL and LOW marks.
14. Stop the engine and tighten the cap. Check the coolant level,
and add water if the level is low.
4 - 24
MAINTENANCE MAINTENANCE