I've been noticing that my CPU has been running pretty hot with the stock fan that came with, and I'm considering a closed system liquid cooler instead of a heat sink. All other components are running at acceptable temperatures and so having a traditional liquid cooling system seems somewhat pointless. What are your thoughts on closed system liquid coolers? What are the pros and cons in comparison to copper heatsinks/air cooling?
It depends on onwhat cpu you got, if it is overclocked and how high is the overclock. Obviously if you have a case that can support it as well. I would say unless you going for very high overclocks then aio isn't worth it. A good mid range aftermarket air cooler will be better. So... what are your rig specs?
i5 4690k @ 3.5Ghz (haven't felt the need to overclock it for anything yet), 2x4GB Ram (can't remember brand) 1600, Radeon Sapphire 5860, 650W power supply, Samsung 840 EVO 250 GB SSD. Have a friend offering to a closed system liquid cooler for $30 though, just trying to figure out pros and cons compared to an air cooler.
Depends on which one your friend is selling you tho. Generally speaking i wouldn't buy a 2nd hand aio cooler. If it was a custom loop and you could actually see whats going on maybe then yes but not a close loop, unless its less than a year old. A high end air cooler (like Noctua nh-d15, Be Quiet dark rock pro3, phanteks ph-tc14...) is better than a cheap aio.
Air vs AIO, air wins every time. Air doesn't cool as efficient at higher temps as AIO but it's hardly enough difference to justify $50. Air is generally quieter, cheaper and more efficient at realistic usage(Playing games). However, heat sinks require maintenance. You really need to get in there and clean out dust buildup at least once a month otherwise that performance will decrease dramatically, to the point where it's not doing shit besides acting like an insulator for your CPU. So if you don't have the time or fucks to clean your heat sink I'd recommend going AIO as it requires near zero maintenance and will perform at 100% even long after your CPU has become obsolete.