@zhaobinis1 I am not sure but one possibility is that the Noctua fan wiring is not compatible with the Dell motherboard wiring. There has been some discussion in this forum that the Dell fan wiring is proprietary and unique to Dell.

Thank you. Only cpu fan is Noctua. The case fan is still stock. Anyways I will try to switch back the stock cpu cooler and see how it goes. 

it looks like 8940 cpu fan header is standard 4 pin.  the pinout should be standard.  there is no Dell proprietary pinout here afaik.

You are absolutely right. Unfortunately it happened to me a few times that the cpu fan and case fan won’t speed up, always at lowest rpm, causing cpu to overheat. It went away when I shut down then turn on. Reboot won’t work. So it makes me wonder if these two issues are related. So far I’m really not impressed with this pc. My biggest complaint, apart from what I mentioned above, is the 3060ti goes to full load so easily, causing loud noise from the gpu fan.This 3060ti goes to full load when playing divinity: original sin 2 at 1440p 165hz, and 80% load at 1080p 60hz. my 8 year old pc with e1230v3 and rx570 (later upgrade in 2019) runs at 40% to 50% gpu load at 1080p 60hz. I barely notice the fan noise on my old pc, partly because the larger case, better air flow, the server cpu, and lower load on less demanding tasks, like the game I mentioned. Serious considering return this pc now.

Do you have similar issues? If not they there must be something wrong with either my system or my motherboard. But I contacted Dell technicians. They just run some basic tests, installed a bunch of software and concluded nothing was wrong. They didn’t even address my specific issue, just standard tests. Quite frustrating. 

If your Dell bios is not throwing a startup error of CPU fan failure, the bios must be reading some within normal limit rpm of the fan.  it is mysterious at this point why HWmonitor does not detect cpu fan rpm.  but if cpu temp is good I would worry about this issue later.   afaik you cannot tweak the cpu fan rpm manually in Dell bios.  so whatever app says of cpu fan speed is just another meter reading that only makes the user feel subjectively better or worse.  I would only care about cpu temp and objective hearing of cpu fan noise.   if temp is good and fan not noisy. I would be content and not stress myself over all the small meters on the dashboard.

The CPU and board fan are named „Other (Docking)“ in section „DELL EC: DELL XPS 8940“ of HWInfo. So they were detected but you can‘t control them.