BoomerD posted. "I don't know the ASUS coolers...they never impressed me, but seems like, if they're plugged into the pump header on the mobo and that's set for PWM in BIOS then it SHOULD operate on variable speed control."
Here are the details of why I advise SOME people (depends on what mobo headers they have) to plug the PUMP into the CPU_FAN header AND make sure to set that header to PWM Mode. It uses a "trick" or quirk of the new PWM design versus older.
Background: the classic 3-pin fan is a DC motor whose speed can be controlled only by altering the voltage of its power supply. Power is by Pin #2 of the header (Pin #1 is Ground), varying from 12 VDC for full speed down to about 5 VDC for minimum speed without stalling. In the 4-pin (PWM style) new fan design, the header signals are as similar as possible to the older design to ensure market acceptability during their introduction. Pins 1 and 3 (speed signal from fan to header) are unchanged. Pin #2 is changed to be +12 VDC always. Pin #4 carries the new PWM signal. The fan motor contains a small chip that modulates the flow of current from the fixed 12 VDC supply line through the windings To reduce the fan speed to whatever that PWM signal requires. (The PWM signal is basically a "% of Full Speed" signal.)
A 4-pin male mobo header can be configured to send out signals in either form. If it is operating in the older Voltage Control Mode (aka DC Mode) the pins supply Ground on Pin #1, a Voltage varying on Pin #2, and it receives back from the fan the speed signal pulse train on Pin #3. Pin #4 has no signal on it. If the header is set to PWM Mode, then Pins 1 and 3 are unchanged. Pin #2 sends out +12 VDC always, and Pin #4 sends the PWM signal. NOTE that this METHOD of sending signals is separate from the setting of the header PROFILE, which is the strategy for deciding what speed the fan SHOULD operate at, depending on a temperature sensor or on some other choice of fixed or custom fan speed.
If the fan type matches the Mode setting of the header, all works as expected. If you mis-match, this is the result. A 3-pin fan receiving PWM Mode signals gets a fixed 12 VDC supply from Pin #2 and gets no signal from pin #4 - it has no line for that. But it also has no special chip, so it cannot modify current flow. So it always runs full speed. If a 4-pin fan is receives older Voltage Control Mode signals, it gets no PWM signal from Pin #4 so its chip cannot modify current flow. BUT the power supply from Pin #2 is a VARYING Voltage so its speed IS controlled just as that of a 3-pin fan. This is not ideal for such a fan design, but it does work. This design yields the best results to simplify introducing the new system to a market full of older fan control designs. If you mix up the fan type and header type, you get either lots of cooling with no control, or fully-controlled cooling.
Next factor: failure. On most mobos all fan headers will monitor the speed signal coming back from the fan for NO signal (sometimes, for a low speed) indicating fan FAILURE. That propmpts an on-screen warning so the user can take action. On many mobos for the CPU_FAN header specifically the actions are more agressive. After a short delay the entire system is shut down without waiting for the temp sensor inside the CPU chip to show high temperatures. This is to protect the CPU from rapid overheating and permanent damage with NO cooling. On many such mobos, the system ALSO will refuse to boot up if there is NO speed signal at the CPU_FAN header immedately on start-up. In the case of an AIO system, of the two elements involved, the PUMP is the more critical on failure. NO pump action means NO heat removeal from the CPU and rapid overheating. On the other hand, if the pump has not failed but one or more rad fans has failed, the temperature rise in the CPU chip will be slower and a different over-temperature protection system will reduce CPU speed to reduce heat generation, and may later shut down completely if the temp continues to rise above a limit. Unfortunately, no mobo manual ever appears to provide details of these protection systems. Further, they never make it clear whether or not other headers like CPU_OPT and AIO_PUMP do the same process.
Now to the case of an AIO system which requires power AND control AND Failure Monitoring of a PUMP and of RAD FANS. IF the mobo has separate headers designed for those functions, that is how it should be done. But some mobos do NOT have a way to control both such headers based specifically on the Temperture Sensor inside the CPU chip, which most certainly IS how the RAD FANS should be done, so those fans need that header. On the other hand, that may be the only header that does the drastic response to FAILURE, so the PUMP needs to be connected to CPU_FAN. Dilemma!
The solution is the Quirk of the results of MIS-match. When necessary, one can use a simple Splitter to connect BOTH the PUMP and all of the RAD FANS to the CPU_FAN header. This is becasue for MOST AIO systems the PUMP is wired just like a 3-pin older fan becasue it is NOT intended to have its speed controlled. So when that unit is conneced to the PWM Mode signals for a header, it runs full speed all the time as intended. But the RAD FANS connected to the SAME set of signals DO respond to the PWM control signal and DO have their speed controlled according to the temperature sensor inside the CPU chip.
There are TWO important items the user MUST do to get this to work. First, when connecting to a Splitter, that unit will send back to the host header the speed of only ONE device, and in this case that MUST be the PUMP speed to monitor for failure. So the user must identify the Splitter's only output connector able to relay the speed signal and connect the PUMP there. This does have the side-effect that the header can NOT monitor for failure any of the RAD FANS, so the user needs to check them from time to time.
The other is a MODE configuration setting in BIOS Setup for the CPU_FAN header. It is essential that this header output signals in the newer PWM Mode, so that option must be set. Many such headers now have an option for Automatic Configuration of Mode and this must NOT be used for this case. In that Mode what happens at every boot-up is that the header starts in PWM Mode and notes the initial "fan" speed. It then sends out a PWM signal for slower speed and checks the result. If the speed did NOT reduce, it concludes that this must be an older Voltage Control Mode (3-pin) "fan" and changes its MODE to that. Now a PUMP will do exactly that (NOT reduce its speed) so the header WILL change toVoltage Control Mode so it CAN reduce PUMP speed, and that is exactly what we do NOT want. So the MODE must be set to PWM.