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How much do I need to worry about the liquid in them going bad or clogging things up etc? Looking at some Corsair ones right now and they have a 5 year warranty... I'm assuming this will come in handy if the motor burns out. Anyone know?
In a closed system, any liquid that stays in there is going to stay liquid in there. Unless theres some kind of leak, nothing is theoretically going to evaporate or run dry ever. The first point and most likely area of failure is going to be the pump motor.
If you get an enclosed system from corsair or something, i would feel pretty confident that it will run up to and past its warranty unless, like DeathPrincess said, your pump fails.
Actually, closed loop systems still lose fluid over time through diffusion (I believe thats what they call it). The water somehow seaps through the plastic in a vapor state but its an incredibly low rate.
I've got an H50 thats been running about 6-12 hours a day since March of 2010 and other then cleaning the dust out of the radiator its been performing just as well as the day I bought it. If Corsair warranties the product for five years, then the fluid should last at least five years...though that depends on your line of thought on today's products and their warranties.