Komatsu GD555-5 Operation & Maintenance Manual page 268

MAINTENANCE MAINTENANCE
13. Drain the coolant from sub tank (5), wash the inside of the sub
tank, then add water to between the FULL and LOW marks.
14. Stop the engine, wait for approximately 3 minutes, add coolant
up to the mouth of the filler port, and tighten the cap.
SERVICE PROCEDURE SERVICE PROCEDURE
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