63 Dart overheating issue

Draining the radiator of the coolant mix, removing the lower hose, covering the outlet of the rad, refilling with water to the top, and quickly uncovering the outlet one can see how quickly or slowly all the water comes out. Backyard style diagnosis but you can get a good indication of whether it’s obstructed or not if you’ve done it enough times with new or unobstructed radiators and ones that are plugged up for whatever reason. Works on heater cores as well using a garden hose gauging by how much water comes out the other port as well as how much backs up and try’s to push the spray nozzle away from the hose end your shooting water in.