Temps with H100i Pro dont seem normal

My vr rig: rog strix x470f, ryzen 7 2700x, gtx1070ti, 2x8gb G.Skilll ripjaws 3200, corsair hydro h100i pro, Itb SSD o/s drive, meshify mid tower. There is one stock case fan exhausting out the rear. Windows10. Top filter has been removed. Glass side removed during testing. The pump head was attached to the cpu with Grizzly paste, and its tightened down on cpu fully.

I have a huge differential between cpu with system just idling in windows10, and the cooler water temp. And at end of cpu stress test, there is an even larger difference!

 

Here are test results running Powermax for a 30 min. Stress test. (That is max duration....but temps stabilized well before end of test and werent going higher). I ran amd ryzen master to track cpu temp, and ICue to track cooler temp......

 

Before test: cpu temp 39-49 C. (Varying.....avg was 40)

Cooler temp. (I assume its water temp?) 28.2 C.

 

At end of powermax test: cpu 66C, cooler temp 32.5C

 

Ambient temp just in front of tower was 24 deg.C

 

Why should there be such a big difference?

 

With a peak temp of just 66 deg., can i expect to run any game or sim without heat issues? I use it for RF8 and X plane 11.....my son uses it for various steam games. We have HTC Vive for vr.

I should mention also the tuning in bios is just set for auto. The core clock is varying a bit between abt 3.8 and up to 4.2.

Your coolant temps sound perfectly fine.

 

Peak CPU temp of 66C is, again, perfectly fine.

 

So ... what is the "big difference" that's concerning you?

The difference between cpu temp and water temp before test, and a much larger difference at end of test....30 deg C. The water temp shouldnt be closer to cpu temp?

No, the heat transfer from CPU to cold plate to coolant stream is direct contact type. It would be like expecting the heating element on your stove to be the same temperature as the water in the pot sitting on top of it. In this case, the coolant system is trying to actively release that heat all along, rather than putting a lid on it. A normal idle state for the coolant is +4-7C above the room temperature. Most people will see a coolant rise of +4-8C beyond that during moderate use, depending on CPU design, wattage/load, and fan speed. The cpu temp is of course still important, but that value is substantially determined by voltage and you are seeing the temperature at the underside where the pins meet the CPU. The cooler keeps this from being worse, but it can’t prevent that initial heat creation where the voltage is applied. We are all limited by what the cpu can conduct out, rather than our cooler capacity.

 

With the normal power saving features on (whatever they are for AMD), you may see core temp very close to the coolant temp at idle and the coolant temperature represents the lowest possible cpu temp. However, modern cpus never seem to sit still, so it’s a bit of a fleeting moment. The AMD 2700x seems to idle slightly higher, typical of any large core count cpu.