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macstatic

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Oct 21, 2005
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What's the thickness and size of the thermal pads that go underneath the single-CPU cMP 5,1 heatsink?

I replaced my 2.8 GHz quad-core with a 3.46GHz six-core a few months ago, but didn't know about the thermal pad (which looked a little dry/worn IMHO). Now I'm about to replace the (very noisy!) cooling fan and thought I might as well order new thermal pads while at it. I'm pretty sure fresh, new pads will lower the overall heat a bit.

I think I still have some thermal paste left for the CPU, but in case I have to order some more: are there any differences between the various brands? Any specific recommendations for best possible performance?
 

eicca

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Oct 23, 2014
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I used Arctic MX4 paste on my CPUs when I upgraded. Also used it to refresh my ancient MacBook Pro. The MacBook now runs noticeably cooler so I imagine the cMP does as well. The MX4 stuff gets good reviews.
 

macstatic

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Sounds good!
I see MX4 is sold in various sized syringes (2g, 4g, 8g, 20g, 40g). How much would I need for one Xeon CPU in my cMP?

Actually I also have a Macbook Pro (13" mid-2012 non retina), but didn't know about it using thermal paste -does this apply to all Macbook Pros?
 

eicca

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Sounds good!
I see MX4 is sold in various sized syringes (2g, 4g, 8g, 20g, 40g). How much would I need for one Xeon CPU in my cMP?

Actually I also have a Macbook Pro (13" mid-2012 non retina), but didn't know about it using thermal paste -does this apply to all Macbook Pros?
Yup all laptops will use thermal paste. I bought the 4 gram tube and it was plenty for all three of my processors. The 2 gram would do both your processors if you decide to go all in.

iFixit has a great guide on doing the thermal paste on those old non-Retina unibody MacBooks. Just be real careful and don’t yank any wires like I did!
 

macstatic

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Oct 21, 2005
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Thanks for sharing. Looks like the 4g might be a good choice -that way I can get a 2nd chance in case I need to redo the fan (I'm installing an after-market replacement fan and I've never done it before).

That leaves the thermal pad for the cMP CPU heatsink. Does anyone have any idea of its thickness and size?

PS: I just found this iFixit Mac Pro single CPU Northbridge heatsink repair guide which was quite interesting as it explains more thorough cleaning of the heatsink which I haven't seen elsewhere. There's also a photo (step 11) of the heatsink with the pink thermal pad I'm talking about. It would be useful to know the thickness and size before ordering it and without having to open up the computer twice.
 
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eicca

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Honestly I didn't even know thermal pads were a thing on the cMP. I just used the Arctic stuff.

Is the single CPU heatsink setup different?
 

macstatic

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I have no idea -the only Mac Pro I've used is my own.
UPDATE: apparently not so different when it comes to the thermal pads, according this this iFixit Mac Pro 2009-2012 dual CPU service & repair article:
MorQbbdvAJqQllYs.huge


And for comparison, here's the single-processor heatsink from the other iFixit article I linked to earlier:
Atwrb2SCHVSDKh2G.full


Looks like the heatsinks are different (come to think of it, I've been told the fans are of different sizes as well).

I didn't know about the thermal pad prior to upgrading my CPU, or else I would have ordered a new pad first. Too bad I didn't measure it while I had everything opened up :(
 
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KeesMacPro

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Nov 7, 2019
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It seems to be common to re-use the thermal pad on the heatsink(s).
If i'm not mistaken its for the voltage regulators and it doesnt seem to have a significant influence to replace them...
TBH i never replaced them in my MPs.
 
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eicca

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Oh you're talking about that pink thing along the edge?? I didn't even notice what mine had, and I certainly didn't change them... Haven't had any problems though.
 

macstatic

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Yup, those pink strips. Not sure what they're meant to cool (I didn't take an overview photo unfortunately), but anything that brings down the overall heat is a good thing.

I just found out that I had taken photos of my own CPU upgrade including the thickness of the thermal pads !!! Looks like 1.5mm (or squished 2mm pads).
20200701-133858_P7010002.jpg

20200701-133920_P7010004.jpg

20200701-134054_P7010006.jpg


Unfortunately I didn't measure the length, but with an overview of the heatsink (screenshot below taken from "Apple Mac Pro 5,1 CPU Upgrade Guide | 6-Core Xeon X5690 3.46Ghz" on Youtube) and knowing that the fan width is 8cm I'm guessing something like 12cm and 1cm wide.
Screen Shot_YT_thermal pad cmp.png



What do you think?
By the way, I read something very interesting about applying thermal paste. The person posting claims many people (including Apple when assembling computers) use too much thermal paste which will actually make heat transfer worse than using less! Do you think this is true?
The normal white stuff you see is usually a ZnO (zinc oxide) mixture. And yes, it does the job. However, something like Arctic Silver works even better at facilitating that heat transfer (pure silver is about 10x as thermally conductive as ZnO), so we can move that heat out of the CPU and into the heatsink system.

That's also why it is SO important to have AS LITTLE HEATSINK COMPOUND AS POSSIBLE to fill those voids in the metal-to-metal contact patch. Copper is about 9x as thermally conductive as ZnO, so having too much heatsink compound hurts thermal transfer rate.
 
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GoJohnGo

macrumors newbie
Feb 18, 2022
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Were you able to determine final dimensions?
From your estimates, it looks like one of these in 120 x 20 x 2mm would do two heatsinks.

I have 4 dual and 2 single heatsinks to tackle.
 
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