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Model A1419 / Late 2013 / 3.2 & 3.4 GHz Core i5 or 3.5 GHz Core i7 Processor, ID iMac14,2

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Best thermal paste for iMac GPU and vram chips?


I finally after almost 7 years decided to change thermal paste in my mac, because the fans were loud all the time. It is late 2013 model with i7 and gtx 780m. On the CPU and GPU was classic thermal paste, but on the vram chips was white thermal paste.

I really dont know if I should use thermal pads for the vram chips or thermal paste. I found different opinions on the internet and I am totally lost :(

Should I use thermal pads or thermal paste? I was thinking about Grizzly Kryonaut or Arctic MX-4.

Thank you for the answers. I really appreciate it!

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The GPU VRAM chips need special handling as the gap to the heat sink is greater than the distance the GPU is. This gap is the issue! Standard CPU/GPU chip TIM is designed to fill the micro surfaces of the metal to improve the heat transmission. It is not designed to span a gap!

Think of it like water pressed between two sheets of glass so only a very thin layer is present between.

The VRAM chips have about 1.5mm of gap between the top of the chips to the heat sink. Apple started off with heat pads and then transitioned to special gapping TIM. Sadly, it was a failure! As it just can’t effectively move the heat across the distance. I only use thermal pads on the VRAM chips.

OK, moving back to the CPU & GPU chips …

The differences between the top five thermal pastes are so little it really doesn’t matter! Unless you are pushing your system to the wall every day for long periods. The best way to think this is do you need a tricked out car to get to work every day or are you in the middle of the indy500 race?

I personally use both Thermal Grizzly Kryonaut (12.5 W / mk conductivity) and Arctic Silver 5 (9.5 W / mk conductivity). I use Kryonaut on my pro’s gear and I use Silver on most of my standard users. The most important aspects is being non-conductive or capacitive as that will mess up your chip if it spreads past the area it should be placed.

What is important here is the volume needed is very little! You only want enough to coat the black silicon chip in a laptop or the metal heat spreader on a desktop class chip. You don’t want it to oozing onto the green chip base as it will interfere with the small SMT devices scattered on it. This is why you need to be careful! To much and you’ll chase your tail looking for a non-problem!

Going back to the thermal pads for a sec…

To be safe I dry fit the heat sink on and using a feeler gage (or a few strips of card stock) I measure the gap between the VRAM chips and the bottom of the heat sink. The pad height needs to be this or slightly higher.

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What's the recommended thicknesses GPU thermal pads for:

> iMac 27" i7 3.4GHz, NVIDIA GeForce GTX 680MX 2GB GPU

> iMac 27" i7 4.0GHz, AMD Radeon R9 M295X 4GB GPU

Should it be 1.5mm?

I have Arctic Silver 5...shouldn't I use Arctic Silver 5 on the CPU and in the GPU?

Best regards


@boxerboss - there is no easy answer here as The logic board or MXM board GPU & VRAM chips height dictates what the pad will be needed.

I use a small thickness gage or you can use a collection of card stock strips to figure out the thickness needed.

Basically, I dry fit the heat sink and slide in the gage you want the fit to be snug. Then use a measuring caliber to measure the card stock pile.


In summary... in the GPU cannot be used Arctic Silver 5 (or other thermal paste)... must be used thermal pad...is that?

Bet regards


@boxerboss - No! That’s not what I have stated. The CPU as well as the GPU chips get standard TIM as I posted in my answer. ONLY the VRAM chips get the thermal pads.

Get the two Arctic products or get the two Thermal Grizzly products. The first listed is the TIM the second group are the pads.


OK, although I didn't express myself properly, I was referring to the VRAM

In general, what could happen if Arctic Silver 5 is also used in the VRAM?

Will it be completely unadvised?(the main problem is not being thick enough like K5-Pro to fill the gap?)

These questions are simply to understand if it will also be an adequate use (but not so recommended), or if it will cause an insufficient cooling of the VRAM due to not filling the gap between the VRAM and the cooler, and that causes the VRAM not to cool enough (and for example it may require additional force to push the cooler to the VRAM)

Best regards


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