2008 Toyota Prius Owners Manual - Page 484
2008 Toyota Prius Manual
Page 484 highlights
5-2. Steps to take in an emergency NOTICE n When adding engine coolant Wait until the hybrid system has cooled down before adding engine/power control unit coolant. When adding coolant, do so slowly. Adding cool coolant to a hot engine too quickly can cause damage to the hybrid system. 458 PRIUS_U_(L/O_0802)