AIO Cooler VS Motherboard Fan Control

Well, I'm an idiot. Couldn't figure it why my Corsair H100iGTX couldn't cool well on a new setup (i7 9700K), did some research and found recommendations to set the motherboard fan control to full speed, this greatly improved cooling performance putting idle temps closer to where I'd expect them. I imagine the motherboard control was fighting with the Corsair software, the Corsair software was reporting that the pump was running at its full speed, but I guess it was never really accomplishing that with the motherboard fighting it.

The H100iGTX is leftover from my i7-6700K, it worked fine there, but I'm not sure that the H100iGTX is enough for the i7 9700K. The 9700 sits under 40C while I'm browsing the web, but Far Cry 5 brings it into the 90C range and this is not OC'd. Probably time for a bigger cooler.

AIOs like your Corsair have a pump that requires a full 12v at all times. They can take that 12v and still control their own pump and fans with a PWM signal internally, but they need 12v no matter what. Unfortunately, since they're designed to be supplied with 12v always, they typically come with a 3-pin plug - no PWM wire. Motherboards often see a 3-pin plug and decide "It's a DC fan and I need to control it by varying the voltage!" And then, no matter what you tell the motherboard, you can't change it's mind.

I've seen it happen. My brother's machine absolutely refused to provide full voltage to his H100i, regardless of settings in the BIOS. The stupid thing kept under-driving the pump, and we kept seeing the same things you did - acceptable idle temps and thermal-shutdown load temps.

Plug that thing into a molex or SATA power feed directly from your power supply. Marketing be damned, even modern "watercooling friendly" motherboards are total idiots.

A lot of motherboards now have a "pump" fan header that supplies the full 12V all the time. You might check if your motherboard has one - they're often located near the CPU socket.

RazorWind said:

A lot of motherboards now have a "pump" fan header that supplies the full 12V all the time. You might check if your motherboard has one - they're often located near the CPU socket.

Click to expand...

Mine has two pump headers, I even connected to it once but put it back on the CPU_FAN header. Since you mentioned it, I put it back to the pump header and that appears to have done the trick. Instead of hitting around 95C while playing Far Cry 5, my max temp was 78C and the fans weren't blowing the doors off. Gigabyte's site mentions 'high current fan' support, but the manual doesn't seem to mention the header support (voltage, etc.) so I guess they assume the user knows better.

78C isn't terrible, that should keep me out of throttling range, it certainly keeps me from buying a new cooler soon, but I will eventually buy something more capable.

Adding that temps drop a lot faster after CPU load drops.

It's been a while since I used an AIO, but I don't recall them really blowing me away in terms of how cool they could get the CPU. 78 may be about the best it can do, given the relatively small die size of the 9700K.

Are you overclocking?

My h115i kept a 7820x under 55c locked at r4.6ghz all core gaming all day.
It’s doing a 1700x or a 2600 at edge clocks all core under 45c.

ive used asrock, asus, gigabyte boards and they were all fine with respect to setting pump to 100% and setting a custom fan curve.
They were/are all cheapies.