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A2115 / 2019 / Processors from 3.0 GHz 6-core i5, up to 3.6 GHz 8-core i9. Released March 19, 2019.

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Thermal pad thickness for GPU VRAM? iMac 27" 5K (19,1)

Hi All,

I will be upgrading my CPU shortly so will have to remove the heatsink in my 2019 27” iMac. I’m about to order required parts including thermal pad (GELID) for the VRAM chip but don’t know what thickness pad to buy.

I’m not keen on dry fitting the heatsink and measuring the gap VRAM chip to heatsink with a feeler gauge as some might suggest (as I can be a bit of a clutz and fear damaging board, not to mention the CPU socket in the process).

So, I’m hoping someone here has already done so and knows what the gap width is. From what I can surmise, 1mm appears to be the gap but I have not found any clear or definitive answer as of yet. Please advise.


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You can use thin strips of card stock stacked up to figure the gap Vs a metal feeler gage. Then just use a caliper to measure the thickness.


Thank for your reply Dan but I want to order the pads *before* I take the heatsink off so am asking beforehand. Besides but I don't want to be fiddling around measuring gaps using any method as there is risk in damaging the CPU socket pins (which I have done in the past on another machine)


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OK. So I wasn’t able to measure the VRAM-heatsink gap with card stock or cardboard as the thick thermal paste would not budge, at all. Couldn’t even get a thick plastic sheet in the gap. Luckily, when I removed the h/s, a few clumps of the thick thermal past came away on the h/s intact, and I was able to measure it at a smidge under 1mm so I used 1mm thermal pads when putting the h/s back on.

(As a side note: Clutz me also best about a dozen sock pins, mostly in different directions too, trying to get the RAM shield off. With patience, a magnifying headset, tiny tweezers but also unsteady hands, I was able to get most of the pins back in place … sort of. Amazingly, the new i9 CPU and new 64GB RAM works a charm. )

So, the short answer to my question “Thermal pad thickness for GPU VRAM? iMac 27" 5K (19,1)” is: 1mm.

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You don’t need to take things apart to make the measure. Apple uses a gapping paste these days for the VRAM chips. As such, using the cardboard to push the paste aside is quite doable.

Sorry to say I haven’t repasted the 2019/20 systems yet so I can’t give you a size. Apple also uses a few different sources so its hard to be sure until you open the system. I’ve mostly found the .5 and 1.00mm have been what I’ve been using in the 2014/15 & 2017 systems. Its still a bit early for your system unless you are a very heavy graphics person in a dusty environment. So just get the three: .5, 1.0 & 1.5mm. OR… just get the gapping paste which is not as good. Even some of the pads are questionable in quality.

This is what I use:

And lastly, to add even more to the confusion! The movement of heat is not that straight forward. Here we have a competing GPU chip also sharing the same heat sink surface. So what can happen is the hotter GPU heat can transfer to the VRAM chips, the heat for both is being sucked away by the heat pipe to the fins to be pushed out. So as long as we push the fan higher when its’ clear things are getting a bit warm we can control things. But this is mostly as issue when rendering video’s or heavy image processing and is dependent on encoding and if it’s a CPU or GPU process within the given application.

I strongly recommend getting a good thermal monitoring app like TG Pro which can speed up the fan (turbo) when things are getting warm over-riding the systems fan control at that set point.

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