sorry I was not more clear. does the coolent suffer from any type of seperation or settling over time?
Not likely. In most cases it's just distilled water. Nothing in it to separate or settle.
Some people like to change the coolant every six month or so, and you can find youtube videos on how to. Which you'd need to do if, say, they were leaking.
But I've got a couple Corsair AIOs (an H80 and an H60, iirc) and my temps haven't budged since they were installed (2 years or more? I can't remember now - the systems run 24/7 though), so IME, barring leaks, these are zero-maintenance and should last a long time.