I replaced the elbow in the tentioner and the car temp started overheating fast, on 2000 Chevrolet Monte Carlo

What cause this to break, when this elbow was replaced less then a year ago because it was rotten.

Asked by for the 2000 Chevrolet Monte Carlo
Bleed air from system, there is a bleeder near the thermostat. Be sure it is FULL of coolant. NAPA has these elbow's made from aluminum, part # 6601942. They do not rot!!
Thanks alot. Also just found out the flow of water is restricted to the block.