I recently did a timing belt/water pump change on my own. When I changed the water pump i drained the coolant, and according to my mechanic, I blew my radiator by not running the engine with the cap off after changing the coolant. According to the mechanic this lets air bubbles form in the radiator, which can cause pressure that damages the radiator.
Do I need to run the engine with the radiator cap off whenever I add coolant to the radiator or only when I drain/flush the system?
Also, can I take off the cap to the coolant overflow container and fill that without needing to run the engine with the cap off the radiator?
honda civic 2001