Comment by cameronperot | Hacker News Reader

Comment by cameronperot | Hacker News Reader

I replaced the single pipe heatsink on my T490 for one with dual heat pipes as the single couldn't sufficiently cool the CPU (was hitting 97C out of the box and after several re-pastes). So I set out on a journey to find a good thermal paste to use. However, finding a good thermal paste for laptops (more specifically on die usage) isn't as straightforward as one would think. A lot of the high end thermal pastes work best for desktop use, i.e. between a heatsink and an IHS, whereas on laptops you don't have an IHS so it's between the heatsink and the die. These high end thermal pastes usually all succumb to the same problem called the pump-out effect [1], where after a number of thermal cycles the performance of the paste begins to fall and it needs to be re-pasted.

I ended up going with Prolimatech PK-3 as it's a fairly viscous thermal paste, and it has held up well for the past six months. Although, I have noticed slightly higher max temperatures than when I originally applied it, but nothing alarming.

[1] https://www.overclock.net/forum/28099300-post10.html

I ended up going with Thermal Grizzly's Kryonaut when I repasted my MBP (Apple does such a horrible job on their own). Due to how thick it is, pump-out basically can't happen. It's the thickest paste on the market.

It's designed for sub-zero overclocking (thus, the name), and has thinner siblings, but I chose it specifically how thick it is, and how it has no curing time. Sub-zero overclocks has the worst pump-out effect due to the vast range of temps you can travel.

The pump-out on my MBP with stock paste was absolutely absurd (hardly any paste left on the dies, almost entirely shoved to the very edges of it), but given the past year, it has had less thermal degredation than my tube AS5 historically has (which is near-zero, I just have to repaste it every 5-8 years, or "once per life of device").

Apple's own paste didn't survive 3 years, or basically went to shit right after Applecare ended. Suspect this is on purpose, but, obviously, can't prove that.

Edit: By the way, thicker pastes require a little bit more pressure to get good contact. I suggest everyone get a torque screwdriver that can be set to 0.6 Nm/5-6 lbf to screw their heatsink retaining screws on.

Intel and AMD have pretty consistent recommendations, as do GPU manufactures, and they range from 0.8 to 1.2 maximum. 0.6 is enough to not risk overtightening, and is also enough to make thicker pastes happy; 0.6 is also Noctua's universal recommendation.

Also, Arctic Cooling's MX4 is another popular thick paste (usually for GPUs, not CPUs, seems to be more consistent on large dies) that likes high pressure mounts.

Interesting, I had heard somewhat of a different take from Der8auer (who is associated with Thermal Grizzly). In [2] he explains that Kryonaut is a fairly wet thermal compound and that it does indeed suffer from the pump-out effect, and that in direct die applications like GPUs they recommend replacing it once per year.

[2] https://youtu.be/CCqxE-5Ct3w?t=505

Yeah, I watch his stuff already. He specifically mentions because GPUs are large hot dies. I'd never use Kryonaut on a GPU (I've had very good luck with MX4 on GPUs Ive had to repaste or replace stock coolers on).

Bare die CPUs (laptops, delidded CPUs, etc) don't seem to be big enough to cause issues. I imagine, if I have to repaste the laptop, if it even lives that long (it is from 2012 as it is), it's going to be another 4 years down the road.

Good to know. If the PK-3 ever fails me I'll give the Kryonaut a shot.

Any readers understand how the pump out effect works?

In my imagination, it seems like the less paste you have between whatever is emitting heat, and the heat sink, the better- so long as there aren't air gaps.

I see there are many forum posts where people show that it does not, but it feels like the closer proximity of the heat sink to the hot object should _improve_ conduction!

In theory, yes, you would want just enough thermal paste to fill any gaps between the heatsink and die as the thermal conductivity of the heatsink (e.g. copper) is much higher than that of the thermal paste. Unfortunately, I haven't been able to find much on the internet beyond forum posts and anecdotal evidence regarding the pump-out effect. It would be interesting to see a more scientific study of this.

If the heatsink expands a bit and pushes the paste out, then when it cools and contracts it will pull away and leave a gap.

Did you buy a dual heatpipe off the shelf, or did you fabricate on yourself? I’m quite interested in this mod.

Thinkpads with a dedicated GPU come with a dual heat pipe heatsink, whereas ones without the dedicated GPU don't. So, you can take the heatsink for the former and use it on the latter, given that you make sure to insulate the part of the heatsink that is supposed to cool the GPU (this can easily be done by using a quality electrical tape like super 88 on the bottom side). You can buy the part aftermarket or see if Lenovo is willing to replace yours. The part number for the heatsink I put on my T490 is 01YU186.

I never understood why they don’t just put the dual heat pipe on all models. I run my t460p with gpu disabled, and the dual heatpipe cools the cpu so effectively that the fan is inaudible most of the time.

good thinking

Thank you for the information!

'real' heatpipe manufacturing seems out of reach for most people, the inside surface is processed (etching or diced) to carry heat it's actually fancy

doesn't this apply to GPUs and other non-CPU components?

Yes it does.

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