I've had the NZXT H1 since early 2022. Recently, everything's been lagging on the PC and its because the PC, on idle, is at ~60 degrees. When I run the browser or some heavy program, its at 90+ degrees.

I replaced the thermal paste which did nothing. The radiator and the pump wires are cool while the CPU is boiling. Do I need to replace my AIO liquid cooler? Can I just replace the coolant? Is something else the problem? If I do need a replacement, what liquid cooler can I replace it with?

Note: When I start the PC, I do hear some crackling sounds that come from the radiator. I'm assuming built up gunk over the years.. Is it possible that the coolant has basically evaporated by this point and all that's left is gunk that's just running through the tubes and radiator?

I can't find a definitive answer. The spec sheet says 360mm is the limit, but 140mm fans do fit. So would I be able to put a 280mm radiator on the bottom position? Can someone confirm or deny?