Yea, coolant elbows. The most likely cause of the coolant getting hot when stopped and then going down when you start going is low coolant level, and seeing that you have a leak, 2+2=4, right? So, replace your coolant elbows, refill with appropriate coolant, bleed air from coolaning system, drive the car a couple days and chceck for leaks, and monitor coolant level in overflow jug.