Komatsu PC78US-6 Operation & Maintenance Manual page 110

MACHINE OPERATIONS AND CONTROLS
Checks Before Starting
Do not open the radiator cap unless necessary. When checking the coolant, always wait for the engine to cool down and check
the sub tank.
Immediately after the engine is stopped, the coolant is at a high temperature and the radiator is under high internal pressure.
If the cap is removed to check the coolant level in this condition, there is a hazard of burns. Wait for the temperature to go
down, then turn the cap slowly to release the pressure before removing it.
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OPERATION