Weird maximum fan RPM values after each reboot

[Ri7]

Hi all!
My signature setup (with K4100m) is acting weird about fan speeds.

Each time I turn on my system it shows different maximum rpm speeds for ODD and CPU fans.

With K4100m GPU I really need maximum rpm from ODD fan, but sometimes it shows 3800rpm (that is OK) but sometimes it shows only 2500 etc

I have tried "powermetrics" but it shows "unable to get smc values". Reseting SMC and NVRAM doesn't made any difference too.

I really don't know what to do, but my target is to maximize ODD fan speed to properly cool down my new GPU.

Other info: I use OpenCore without fakesmc (but there is no difference with it), hardware "swap" thermal sensors (odd and gpu heatsink).

Anybody is getting this same behaviour?

 

[Ri7]

I have some news about this issue...

It's apparently related with "ODD" and "GPU Heatsink" sensors.
I guess that when iMac turns on, SMC reads all sensors and store a value for maximum RPM for each fan.

I'm using this solution: https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-29251720

Yesterday I decided to disconnect ODD temp sensor (actually GPU heatsink sensor) and imediately iMac began to set maximum ODD fan speed to 3800rpm (Catalina and Win10). When I plug it back again, random values come back too.

I don't know how this is related with maximum rpm for CPU fan, but as soon I removed ODD sensor plug, CPU fan begins to show always maximum 2100rpm again.

I did several restarts and it's ok. ODD fan maximum possible speed is now 3800rpm and regulated by "GPU Heatsink" sensor with modifications above.

 

[Afro_]

Hi I think I am having the same issue : ( How did you solve it exactly? Just plug and unplug the ODD sensor several times? For the K4100M did you use nicky22's ROM? It seems that macs Fan Control cannot read my K4100M GPU temperature. Did you do something special to get the GPU temperature reading? Thanks for the help in advance.

 

[Ri7]

Hi!

Yes, I'm using nicky22's ROM from post #1 for my K4100m and OpenCore to use UEFi Windows 10 in another SSD.

I'm using sensor solution from audasportler (link above), that is fitting ODD sensor directly on GPU heatsink and plugging it do motherboard.

But the only way I've found to achieve maximum fan speed was unplugging ODD sensor at all. Otherwise each time I boot it shows different maximum speeds for ODD fan.

My advice is to use GPU Heatsink or ODD sensor (if it is on heatsink) to control Macs Fan and unplug ODD sensor connection. It causes fan to blow when you turn on your iMac, but I think it's way more safe.

 

[Afro_]

Hi!

Yes, I'm using nicky22's ROM from post #1 for my K4100m and OpenCore to use UEFi Windows 10 in another SSD.

I'm using sensor solution from audasportler (link above), that is fitting ODD sensor directly on GPU heatsink and plugging it do motherboard.

But the only way I've found to achieve maximum fan speed was unplugging ODD sensor at all. Otherwise each time I boot it shows different maximum speeds for ODD fan.

My advice is to use GPU Heatsink or ODD sensor (if it is on heatsink) to control Macs Fan and unplug ODD sensor connection. It causes fan to blow when you turn on your iMac, but I think it's way more safe.

Thanks for the reply! I am not using OpenCore so that is why then. I am doing the same by just relocating the ODD sensor to the heatsink. Will try your method later to see how it works!

 

[Ri7]

I've tested with and without OC and found the same behavior.
The only way I found to achieve 3800rpm was disconnecting ODD sensor plug from motherboard.

I think there is no difference if you use ODD sensor or heatsink sensor since it's working well.

I'm using "PSU Primary sensor" to control CPU fan. Automatic uses very low speed and my PSU remains burning near 60 degrees. With this setup PSU is always between 40/45°C. I really don't recommend this settings if you use CPU intensive apps.

ODD Fan - GPU Heatsink (50°C/70°C)
HDD Fan - SSD sensor (55°C/75°C)
CPU Fan - Psu Primary (40°C/50°)

Screenshot of my system with only internet browsing.