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Comment by hnuser123456 | Hacker News Reader

Please do some measuring of core temperature response to load before and after re-pasting / upgrading the thermal compound. Something between a large grain of rice and a pea, and I like to clean the CPU and cooler cold plate completely, paste the CPU, then press and smear around the cooler onto the CPU before mounting it, to ensure full surface area coverage with a thin layer of compound.

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As it happens, I did this morning!

I switched from years old Arctic silver 5 to Noctua NT-H1. It resulted in a dramatic difference. 64c loaded vs 84c -- I now suspect I had an air bubble which may invalidate the initial motivation for the work in the first place :-)

The first thing I noticed was that your idle temperatures are exceedingly high, especially for an AIO. My air-cooled ryzen 5 idles at around 35c with nearly zero fan speed on a $30 air cooler.

Most AIOs need servicing after a few years- find instructions on how to disassemble yours, clean the water block, flush the radiator, and refill with a deionized-water/glycol mix.

Genuine question: I've known the law of "pea sized amount" for thermal paste for 20 years or so. Does it still hold true for modern (and larger) CPU dies? I haven't upgraded in a long time so genuinely don't know, but also wouldn't want to use outdated knowledge!

You want to use as little paste as possible while fully covering the heat spreader.

Most modern coolers will provide sufficient pressure to spread a pea sized amount of thermal paste to cover the whole cooler.

There are also thermal pads, both reusable and single use, that perfom well and don't require any guesswork.

If you want to paste, noctua has the best paste in terms of thermal resistance, but mx4 or mx5 both perform well, as does cryorig and a bunch of others.

>You want to use as little paste as possible while fully covering the heat spreader.

The data disagrees. Too much paste is fine; too little is not.

https://youtu.be/EUWVVTY63hc

Yes, but that's not what I said. Too much paste makes a mess, too little makes, well, a different mess. A pea sized amount is plenty, being that a pea is fairly large.

Personally, I do an X if I'm not lapping, but that is more complex and a dot works just fine for most things.

pea-sized is against noctua's own recommendation for AM5. they recommend dots in each corner and a bigger one in the center. [1]

also, Kryonaut is one of several high-performance thermal pastes that outperform NT-H1 and even NT-H2, but they require regular (~1 year) re-application. Noctua paste values stability over performance in this regard.

though if you need stability and performance, nothing really beats Honeywell PTM7950, even on a desktop chip.

[1]: https://faqs.noctua.at/en/support/solutions/articles/1010003...

Video with spread patterns under transparent plate:

https://www.youtube.com/watch?v=wn2ln04dquM

I've seen reports and debates that modern heat spreaders are too large for the pea method, and that an X pattern is more common now.

Here's one of the test videos you can find on Youtube about the subject: https://youtu.be/aaxBYrZFJZM?t=199

Thanks for posting an actual test rather than perpetuating tradition without verification

Science!

Giving a single moment of thought to what happens when the paste is squished to this should lead everyone to the conclusion that a square that is equidistant from the edge to the center is the right pattern with maybe a dot it the middle for piece of mind.

That wasn't tested there.

A square is closed and will probably result in a bubble of air being trapped.

You don't have to close it nor do you have to put it on straight down.

It's pretty easy to get this right by using your head rather than following some ethos.

Youtube recommended a similar video where they tested various patterns. Spreading paste over the the whole heat spreader resulted in a small air pocket, while the same method with an additional paste dot in the middle didn't have such issues. But at that point maybe you're getting too much paste instead, as mentioned you want as thin layer as possible. At the end of the day, it probably doesn't matter much anyway.

I clicked eagerly and appreciated the approach but not the analysis of the results. The only judging criteria was "coverage" (enough but not too much) but no thought was given to thickness, and some application patterns lend themselves to thicker results (just compare the five dots pic to the full coverage or three lines pic). You can see from the results that the "winners" have a fairly thick layer of substrate. You want the absolute thinnest layer of thermal paste that will achieve full coverage.

You need to understand what is thermal paste is used for and then you would understand what for the most of the time pea size is okay.

It's just a compound what helps with a heat transfer. Both CPU IHS and the radiator are not ideal surfaces, so if you install one on one without TP then there would be bubbles of air trapped in imperfections of the surfaces. They are not a problem per se but they do make the heat transfer worse, so IHS is hotter than it could be and a bit less effective to transfer the heat to the radiator.

You have two options to improve the heat transfer:

a) polish both the IHS and the radiator to a perfect surface, ie they would should mirror like; and then you should use a torque screwdriver to ensure what the cooler is tightened and leveled exactly right;

b) or you can just slap some thermal paste between them and call it done.

And in the second case you need 'just enough' of TP to smooth out the imperfections, but if you slpat too much then again you are making the heat transfer between the IHS and the radiator worse.

So if you ever find yourself minding about how much TP should you use then just start with a pea size, place the radiator (you can even screw it if that's your jam) then remove it and look at how the TP spread around the IHS. If it covers 90% with a thin film (and your radiator isn't the lowest shit tier polished with the old rusted raspel) when you are fine enough.

The only difference between 20yo and now is what IHS are way more larger so now you may find a need to use... a larger pea as a reference.

It depends how much you care about tidiness/perfection. Unless you use a metal paste, the worst that can happen with too large amount is that it will leak outside. And you can wipe that - that's it. So feel free to use too much and just clean up afterwards. That's better than using too little.

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