Weird 5800X3D undervolting issue with temps

[SoundsGood]

I've applied an undervolt to my 5800X3D by setting a -0.15 VCCDR offset in the BIOS.
This caused the system to refuse to boot, so I removed 1 stick of RAM and it booted, the CPU idle temperature is much improved at around 40c.
I put the stick back in and now it boots ok, but the idle temperature has risen to around 55c!

I've repeated the process 3 times with slightly different VCCDR values, but every time the temperature is dramatically higher with the 4th stick of RAM installed.
Has anyone else seen this behaviour before?

Motherboard: ROG Strix X570-F Gaming
Memory: 2x32GB (CMH64GX4M2D3600C18) + 2x16GB (KHX3200C16D4/16GX)
Cooler: Noctua NH-D15

 

[SoundsGood]

Just tried with PBO tuner and the issue is apparent with that too .
I looked into getting a couple of 64GB sticks to replace the current 4 but can't find any for sale.

 

[SoundsGood]

I've sort of realised there's not much point comparing temps as we'll all be using different fan curves and I'm also running Linux with several VMs so the base load is fairly high.
I'm going to get a case with more airflow and a 360mm AIO, then maybe look into getting 4 matched sticks of RAM.
For now I am capping the CPU to it's base clock overnight which saves some power and brings it down to just above 33c.

 

[SoundsGood]

I don't think you need to get a new CPU cooler. An Noctua NH-D15 is basically the best air cooler out there so that's not the issue. I am running an old Cooler: Noctua NH-D14 on mine with no issues.

What case do you have? You want something with high airflow. I have a Phanteks P400a.

I also run 4 sticks of 8 Pack ram which are at 1.45v.

You need to set your voltage offset using the curve optimizer. Start at -30 and go down in -5 increments untill it is stable.

Other than that what issues is the high heat causing you?

Also flash the latest bios.

You could also look at setting the power limits on the CPU such as in this video:

You're right that I don't need to swap coolers, the temps aren't affecting me at all but I want to have it running as well as possible and get a new toy to play with .
The case is an NZXT 510, looking at replacing it with a NZXT H9 Flow. Another factor that doesnt help the temps is I have 2 GPUs (3090+1080Ti).
Currently running with PPT limit 100, TDC limit 70, EDC limit 100, -30 curve and its been perfectly stable , maybe worth pushing it a bit more.