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I’m posting this here because maybe someone can answer my question.
I just finished upgrading my radiator. (liquid-cooled GPU, air-cooled CPU.)
I have a flow detector inline, and the pump ran as expected when I disconnected the CPU power and GPU power cables, and had the motherboard jumper connector attached to the 24-pin cable. (This removes power from the CPU, GPU, MOBO fans, RAM, etc. but still allows the pump to run.) Useful for flushing a loop.
I just put everything back together and powered the system on. I don’t see any flow at all. I know the pump is getting power, because if I disconnect the 24-pin cable, and reattach the jumper, I see flow.
There’s a temp sensor that runs through iCue that controls the pump speed. I verified that the pump fan is connected to the correct jumper on the MOBO.
Maybe I have to be booted into Windows, so iCue can be running before the pump will run? I know there’s liquid in the water block and the rest of the loop, but how long before that heats up and damages my GPU without flow?
I can’t say that I’ve paid much attention to the flow detector while the computer starts up. But it troubles me that I could leave the system running for a minute or more normally and not see anything.
I’m really puzzled as to why the pump isn’t running immediately, but does when I use the 24-pin jumper. I mean, it’s connected directly to the power supply. Shouldn’t that power be applied as soon as I turn the computer on?
Do you have a voltmeter? You could probe it and see if you have voltage when you’re expecting to have voltage.
Have you booted into Windows, let Icue start then check the pump to see if it is running?
Is this AIO or custom?
If the latter, what’s the pump attached to on the MB and can you check the speed of that in BIOS?
Corsair XD5 pump/reservoir combo.
No. I was nervous about letting it run without seeing any flow. I know that bootup puts very little load on the GPU, but it still concerned me.
The thing is, when I bypass the motherboard (and its pump fan header) by using the 24-pin jumper, the pump runs. So I know for certain that the Molex coneectors have power. It’s just that they don’t supply power when I first start the computer. Something is stopping it. I’m guessing the pump won’t run if the header isn’t active until the BIOS is loaded. But that’s just a guess.
Custom loop. There are three leads coming from the pump:
- 2 separate Molex connectors directly connected to the power supply.
- 1 attached to the ‘Pump Fan’ header on the motherboard.
The pump speed is controlled with a curve in BIOS. I haven’t let it boot to BIOS yet. That’s the next step - since it’s really the only thing to try next.
On my 7900xtx, the air cooling fans (3) never even run when I’m just in Windows. The fans only start up when I’m in a game and obviously putting stress on the GPU.
You shouldn’t need to worry about GPU temps if you just boot into Windows.
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I have to travel today for a job, but I’ll run fire it up (pun intended) tomorrow and report back.
I’m hopeful that problem I see comes down to the pump controller not being initialized until the BIOS loads, and that the lack of flow when I first start the computer (spinny thing doesn’t move) is something that’s always been there, but never noticed.
What’s this got to do with MSFS?
I’m dead certain that’s it! 
Final update. I booted into BIOS, and the pump was running fine, albeit only 850 RPM because the PWM curve I’d set was so low at low temps the flowmeter wasn’t spinning. I ended up moving the pump to iCue and set it up with a more aggressive pump speed profile. All is well.
Thanks everyone for the advice!
If anyone is interested, here a link to the entire saga I posted this morning.
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