Relevant parts:
Ryzen 3950x
NZXT Kraken X73 360mm AIO (yes, I know it's overkill for just a CPU, but it was the only thing available at the time that wasn't ridiculously overpriced)
Noctua thermal paste
Under idle, CPU temps bounce between ~38-55C, and liquid temp stays at a constant 28C. Under a stress-test load or while gaming, temps stay constant at exactly 51C but liquid temp can raise 1-2°; fans and pump seem completely unphased. and barely change. This is rather odd and I cannot make sense of this and it leaves me with a lot of questions. Why is the idle temp so jittery while load temp is so constant? Why is the load temp (sometimes) lower than the idle temp, despite no apparent change in cooling capacity (remember, fans and pump stay near constant)? Why is it idling relatively high to begin with?
At first I thought it was because of an air bubble trapped in the block or something. I tried moving the radiator around to help remove any stuck bubbles that could be there and saw no change. Then I tried removing the block and reapplying thermal paste just in case it wasn't making good contact and again saw no change. Neither of those should result in the behavior I'm seeing, but who knows.
Since the load temps are good, I'm not too worried about it. Should I be?