4.1/5.1: CPU + ProcHot temp ?

[Lenny_]

- temperatures in Celsius
- Mojave
- 2 x 3,46 GHz 6-Core

When the system is idle it looks like this:

I read that this is a normal temperature distribution: CPU A is warmer than CPU B because the air flow has to go through the heat sink of CPU B first.
Until now I was under the impression that CPU(Tdiode) temp + Relative to ProHot = max operating temp for the CPU:
- CPU A: 44 + 60 = 104
- CPU B: 36 + 71 = 107
For what ever reason CPU B does have a higher limit.
Fan speeds look normal too:

Until here I'm not concerned, but ...

...when Final Cut does some coding and rendering:


the CPU temps look like this:

Now CPU B is warmer than CPU A ... and the max operating temp seems to be significantly lower:
- CPU A: 75 + 23 = 98
- CPU B: 82 + 2 = 84

The Relative to ProcHot value for CPU B even fluctuates quite a bit:

Here it shows: 83 + 8 = 91
Whereas CPU A is still: 71 + 26 = 97

The fans go full speed during this condition:


When the coding/rendering is done the temps go down in a second ... and the fans spin down as well.

Is there something wrong with CPU B? Why does it seem like the max temp is so much lower under load?
Is CPU B and here the very little tolerance to max temp the reason for the fans to go full speed?

 

[w1z]

You need to re-paste the cpus as the difference between diode and heatsink is high, especially under load.. typical values are 1C to 4C degrees when idling and 4C to 6C under load.

I recommend the IC graphite thermal pad as you won't have to worry about re-pasting in the future. Another good graphite thermal pad is Thermal Grizzly's new Carbonaut pad.

Edit: If you are the adventurous type and want the latest and best TIM (thermal interface material) then try the aluminium foil with phase-change coating KU-ALF 5 - 220 W/mK

https://www.enika.eu/ku-alf5-0h-ks-57x122mm-l-al-foil_z23029
http://www.j-rep.com/download/kunze/7phasechange.pdf
https://imgur.com/a/2QOXu2v

I'll probably give the foil a try seeing it performs much better and is cheaper than the aforementioned graphite pads.

 

[Macschrauber]

Are the CPUs delidded ?

 

[Lenny_]

Are the CPUs delidded ?

This computer was originally a 4,1: yes, of course. This will make the application of the electrical conductive thermal pad a little tricky, yes? I don't want to short out something...

 

[w1z]

Good question - I'm not sure about the 4,1's installation process as I am using the IC pads with an original 5,1.

If you are worried, then stick with the regular paste but choose the top-end ones.

 

[Macschrauber]

In another thread some fellow used the square plastic spacers but did not cut all the glue under the delidded xeons. So the CPU has not proper contact with the heat sink.

Maybe worth a look.

 

[Lenny_]

I would not have thought that applying new termal paste does have such an effect:
I did re-paste the CPUs (and the northbridge as the coolers were disassembled already) -> everything is back to normal!

This is the material I used:
Noctua NT-H1

 

[JedNZ]

I'm going to replace the rivets in my Northbridge of my cMP 4,1>5,1(I only replaced the one that was broken about 2 years ago and want to do them both now so that they're the same), and give my machine a jolly good clean up, including re-applying the thermal paste on the NB and the CPUs.

What recommendations do you have for thermal paste/pads? My cMP has delidded CPUs (2 X5680), and I've only ever used Arctic Silver 5 in the past. I don't want to experiment - I want something that is tried and tested to work. I've watched a couple of YouTube videos and read some technical stuff, but it's all over my head working out what's best for my cMP - I feel I need to complete a computing degree first just to understand the lingo for all the thermal products out there and can't tell which one is the best.

I do have a slight amount of technical ability (I delidded and installed CPUs on both my 4,1>5,1, plus my trusty old 1,1>2,1. I've also replaced one NB rivet and did the thermal paste on the NB heatsink, and I've upgraded to a PCIe WiFi ac/BT4 combo card and did the USB wiring so it connects to the BT connector on the mono (rather than buying a kit from OSXWiFI) so have some confidence in my abilities.

 

[w1z]

@JedNZ Thermal Grizzly's Kryonaut is what I would recommend for paste-based applications on CPUs, NB and GPU chipsets.

Edit: it comes with an applicator tip that aids in applying a thin and even layer

 

[JedNZ]

That @W1SS. Confirm it's safe to apply direct to a delidded X5680 CPU (i.e. it has had the IHS removed)?

And does anyone else have any experiences (good or bad) with Thermal Grizzly's Kryonaut? I just want to do my due diligence before I go ahead with it.

 

[w1z]

That @W1SS. Confirm it's safe to apply direct to a delidded X5680 CPU (i.e. it has had the IHS removed)?

And does anyone else have any experiences (good or bad) with Thermal Grizzly's Kryonaut? I just want to do my due diligence before I go ahead with it.

Yes, it is safe on delidded CPUs too.