Asus Maximus 7 Hero: CPU_OPT fan only spin up at 100% load

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Daniel Woodward

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Jul 31, 2014
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So i bought a maximus 7 hero for my new rig, along with a shiny new 4790k and a Cooler Master Nepton 280L cooler. But my problem is that the fans on the cooler only spin up(Even when they do its only at a low RPM) when the cpu is at or near 100% load. The tempratures are fine, the coolers been doing a good job cooling passively but i want the fans to spin up at a little lower temp like 40C or 45C instead of 80C.

Ok so to the root of the problem, i can not change the fan curve on CPU_OPT fan header because there is no fan options for that hedder in the bios. If someone could give me a suggestion as to what to do to gain control over this fan header instead of the default curve, that would be great, thanks.
 
Solution
Karadjgne
Most asus boards have no control over cpu_opt, 3pin or 4pin, its basically a 100% dedicated 12v that will read rpm. Swap the pump from cpu_fan to cpu_opt as the pump will be 3pin, and put the fans on cpu_fan. This is entirely backwards from the directions, but it works just fine. The only reason manufacturers say to put the pump on cpu_fan is because they are betting on the pump failing before the fan does, and setting off the cpu-fan low rpm alarm. As long as you monitor your temps, it wouldn't matter either way, if 1 breaks, temps still rise.

Then check the settings in bios. Since the pump is 3pin, you'll have had no control over cpu_fan header, the motherboards usually only give control to pwm fans (4pin) not analog (3pin)...
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endeavour37a

endeavour37a

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Feb 25, 2013
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The CPU_OPT header is controlled with the CPU header. The CPU header reads the RPM of the fan, the OPT does not, the PWM signal is the same to both headers, they are wired together. So you only need to set the CPU fan curve and the OPT fan should operate just like it.
 
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Daniel Woodward

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Jul 31, 2014
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The CPU_OPT header is controlled with the CPU header. The CPU header reads the RPM of the fan, the OPT does not, the PWM signal is the same to both headers, they are wired together. So you only need to set the CPU fan curve and the OPT fan should operate just like it.
Click to expand...

But the CPU fan header is at full speed and the fans only spin up at 100% load and even then they are only at 500rpm when they are rated for 1500. The fans are noctua NF-A14's
 
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RetroSA

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Jul 18, 2014
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I'm using almost an identical setup as OP and having the same issue. 4670k and nepton 240m with a maximus vi hero.

I followed this guide to set mine up which says pump goes to cpu_fan and fans connect to cpu_opt header via Y cable:

Guide I used to set up.

I have also swapped the stock fans for two Noctua NF-F12's

Same thing as OP, I have no control over the cpu_opt header. Even using AI Suite 3 it shows the cpu_opt header as yellow and running at 0RPM. I've had it loaded up and running at 65C for extended periods with no fans pushing through the rad. I know it's a reasonable temperature, but still, like OP says, it would be nice to have it run cooler if it can.
 
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Karadjgne

Karadjgne

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Dec 26, 2012
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Most asus boards have no control over cpu_opt, 3pin or 4pin, its basically a 100% dedicated 12v that will read rpm. Swap the pump from cpu_fan to cpu_opt as the pump will be 3pin, and put the fans on cpu_fan. This is entirely backwards from the directions, but it works just fine. The only reason manufacturers say to put the pump on cpu_fan is because they are betting on the pump failing before the fan does, and setting off the cpu-fan low rpm alarm. As long as you monitor your temps, it wouldn't matter either way, if 1 breaks, temps still rise.

Then check the settings in bios. Since the pump is 3pin, you'll have had no control over cpu_fan header, the motherboards usually only give control to pwm fans (4pin) not analog (3pin), swapping them will fix that. Cpu_fan should now be set to whatever curve you want (silent/normal/performance), and if for some funky reason you do open up control of cpu_opt, disable or set duty cycle to 100%, which should run the pump at 100%, or @2000+ rpm.

Personally, when I had my Asus board I set it up that way and set all fans to performance, then when Asus fan Xpert2 kicked in, I used that for control, with an alarm on cpu_opt set 150rpm lower than normal running 100% duty cycle.
 
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