DukeChangWang :
I have a 4790k with a Corsair H100i closed loop cooler, but for some reason when it's idle it sits around 40 degrees Celsius, which I saw is not too high but isn't exactly normal either. Also when I record or just play PUBG, the temperature can go up to between 70 to 90 degrees. Do I need to reapply thermal paste or something? I can feel my computer getting extremely toasty in my room when I start to play games, I have a MSI Gaming 5 z97 mobo and a NZXT H440 case.
Is this a new installation of the H100i? If so, I'd remove the block, inspect the CPU installation, as well as the paste itself. If everything is good, reinstall the block ensuring to use a cross-pattern so that there is equal tension applied until snug/not too tight.
I'm not sure what the install instructions say for the H100i, but I use the H105 and have the pump directly connected to the/a PSU power cable, so the pump is running at 100% constantly... NOT variable. This ensures a consistent pump operation and cooler temps. However, if your manual states different, it's up to you on how to proceed on this.
Also, how do you have the H100i fans directed? Intake or exhaust? Intake bringing cool air across the rad, exhaust bringing the case air through the rad. I'd advise using the fans in an intake configuration if not already doing so, as drawing hot case air across the rad is doing your AIO no favors by increasing your CPU temps even if slightly; every degree counts. But again, this is your option.
As a note I'm OC'd at 4.7 and idle at 23*C and operating during gaming averages around 47*C.