250,000kms but you can use coolant test strip to determine that. I wouldn't want to leave coolant in the engine with a high pH level.... http://www.autodork.com/ENGCOL-Coolant.php
Both GM and Chrysler V-Style engines always have leaks. Not a big issue though but look for milky coolant.... http://www.autodork.com/ENGCOL-Coolant.php