Toyota PRIUS Owner's Manual page 653

NOTICE
■ When adding engine/power control unit coolant
Add coolant slowly after the hybrid system has cooled down sufficiently.
Adding cool coolant to a hot hybrid system too quickly can cause damage to
the hybrid system.
■ To prevent damage to the cooling system
Observe the following precautions:
●
Avoid contaminating the coolant with foreign matter (such as sand or dust
etc.).
●
Do not use any coolant additive.
PRIUS_OM_OM47A31E_(EE)
7-2. Steps to take in an emergency
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