iMac CPU Upgrade And Thermal Paste

[Khaleal]

Hey

I'm interested in upgrading the CPU in one of my iMacs (27" Late 2012) from i5-3470S to i7-3770. I'm getting the i7-3770 secondhand for $100 and will sell the current i5-3470S for about $50, so total upgrade cost is about $50 (well, $60 if you take the screen adhesive kit into consideration).

I've opened this iMac in the past for SSD upgrade (now it has 256GB SSD and 1TB HDD, no Fusion Drive configuration). So I won't have any difficulties opening the machine, as I've done that in the past and have the appropriate tools.

I've watched some Youtube videos and read iFixit guides, and at some point I'll need to remove the heatsink in order to install the new CPU. Upon removing the heatsink the thermal paste will break and I'll need to re-apply it.

I've noticed that Apple uses regular grey thermal paste for CPU and GPU, but uses a white-ish paste on the GPU VRAMs which can be seen in iFixit guide (step 60): https://www.ifixit.com/Guide/iMac+Intel+27-Inch+EMC+2639+CPU+Replacement/19630

Does anyone know what thermal paste I should be using on the VRAMs? I have Arctic MX-4 and Noctua NT-H1 which are considered high-end pastes. Will they work well?

I appreciate any help/input.

 

[_Kiki_]

Arctic MX-4 isn't good

When I upgraded CPU in my Retina 5K I used Thermal Grizzly Kryonaut

On VRAM you can replace paste with thermal pads, I think 0.3mm thickness should be fine

 

[Khaleal]

Arctic MX-4 isn't good

When I upgraded CPU in my Retina 5K I used Thermal Grizzly Kryonaut

On VRAM you can replace paste with thermal pads, I think 0.3mm thickness should be fine

Thanks for your input.
Based on what you say Arctic MX-4 isn't good? I've been using it in my PCs for years and it performs very well. I've seen tests and the difference between MX-4 and thermal grizzly is marginal.
What's special about Thermal Grizzly Kryonaut compared to MX-4 or NT-H1? Does it have better specs or just the brand name is better?
When you upgraded your CPU, did you apply thermal paste on the VRAMs or used thermal pads?

 

[_Kiki_]

Arctic MX-4 - Thermal Conductivity: 8.5 W/(mK)
Thermal Grizzly Kryonaut: 12.5W/(mK)

I'm not sure about Noctua, I never used and I can't find spec of thermal conductivity

I used paste on VRAM, but after I assembled iMac I realised, I should use thermal pads (I remember this solution from gaming laptop), so thermal pads will go in next time to iMac VRAM when I find some time to apply them

 

[Khaleal]

Arctic MX-4 - Thermal Conductivity: 8.5 W/(mK)
Thermal Grizzly Kryonaut: 12.5W/(mK)

I'm not sure about Noctua, I never used and I can't find spec of thermal conductivity

I used paste on VRAM, but after I assembled iMac I realised, I should use thermal pads (I remember this solution from gaming laptop), so thermal pads will go in next time to iMac VRAM when I find some time to apply them

Does that mean that VRMs started overheating/temperature increased after applying thermal grizzly on the VRMs?

 

[_Kiki_]

Does that mean that VRMs started overheating/temperature increased after applying thermal grizzly on the VRMs?

no, they are fine, but using thermal pads will be more professional

I recommend also Macs Fan Control if you don't have

 

[cynics]

I second @_Kiki_ with the Grizzly Kryonaut. I prefer it on an iMac because of how inaccessible the CPU/GPU are. Plus since you can't add a larger heat sink you want as much thermal transfer as possible.

However I don't think MX-4 is that bad....just not as good. I'm pretty sure its better than whatever Apple originally had on there. If I had a tube laying around I would probably use it.

I wouldn't replace thermal paste with pads though.

First, they aren't as efficient as paste/grease. Second, you can create a gap over other components if your not careful depending on the heat sink design. You can't "smash" a pad as flat as paste can be and if the VRMs are close enough to the GPU there is the possibility the additional height will prevent a side/corner of the heat sink from being as flat as it could be on the GPU. The opposite applies too, if you replace a pad with paste the heat sink may not have been designed to close that gap as tightly as needed for the use of paste.

On graphics cards you'll often see thermal pads used on the memory/VRM but as a secondary means of cooling. For example on the 1080ti they use thermal pads between the front and black plates but not touching to the heat sink itself.

I don't know the layout of your iMac so it could be a moot point. However I don't see a need to reinvent the wheel here. If they used paste you should, if they used pads you should.

 

[b06tmm]

I used K5 PRO thermal paste on my mid-2011 video card.

"K5-PRO is a high quality gummy / sticky thermal paste designed for use on memory chips and GPUs of various computers including Acer Aspire 6930 , Apple iMac A1311 video boards. This is the only comercially avaliable product at the moment that can replace the gummy thermal paste that is originally used by Apple."

https://www.amazon.com/gp/product/B00UTX7K2E/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1