Question Thermal paste too viscous?

alexprokop

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Feb 17, 2009
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I've recently been tinkering with an old X58 setup with a core i7 920. It's been in storage for a while and when I first booted it up again I was getting temps of around 70 degrees idle -> 100 degrees under load. I reseated the fan/heatsink and applied some new thermal paste from a brand new tube of arctic silver 5. Temps went down to 45 degrees idle -> 75 degrees under load so I was happy enough.

I decided to upgrade the CPU with a second hand Xeon X5680, so I removed the fan/heatsink and was a little surprised by the pattern of the paste underneath (see photo). It seems like in some areas it was quite thick and in others it hadn't spread out at all. Is this OK or should I get a new tube?

I don't have much experience doing this, but the paste was much more viscous than I expected as I was applying. I tinted both the heatsink and CPU with a credit card first and then applied a pea sized blob to the heatsink before setting.

 

PC Tailor

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I'd just ensure that you wipe down all surfaces cleanly before applying. How old is the thermal paste?
Ultimately if it kept your temperatures down, it won't matter. If it worked, it worked.

There are some air pockets which might just be debris or contamination, or just how the cooler was seated, but again, if you had normal temps, then no real need to worry, just eliminating them might help heat dissapation even more so.

The edges of the CPU are where heat disspates the least generally, so it's not so much a problem that the edges of it aren't covered, just as long as there is pretty good coverage.

But the point remains, does how the thermal paste sit make a difference - yes. BUT if it worked, then it worked, no worries. It kept temperatures down, just apply it next time and see, if you get skyrocketing temperatures then you know to retry with maybe new paste.

If the paste is old or exposed to air for too long, i'd be tempted to replace anyway, but by the sounds of it, that's not the case.
 
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I still use AS5 for the bare dies it was designed for, such as GPUs and laptops. However it's too thick for use with an IHS unless you use some rather extreme pressures when mounting.

Remember you want that layer of compound to be as thin as possible because while it may transfer heat much better than air, it's about a hundred times worse than the metal in the heatsink. It's only intended to fill tiny air gaps where two surfaces aren't perfectly smooth.
 

alexprokop

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Yes, I'll clean it down with isopropyl alcohol and lint free cloths. The heatsink pad is circular anyway so it seemed to spread around OK, it was the air pockets I was concerned about, but it makes sense that as long as temps are OK it's working well enough. I bought the AS5 very recently from a local computer parts store but who knows how long it was sitting around there for.

What alternative pastes would you recommend that are less thick?
 

PC Tailor

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Yes, I'll clean it down with isopropyl alcohol and lint free cloths. The heatsink pad is circular anyway so it seemed to spread around OK, it was the air pockets I was concerned about, but it makes sense that as long as temps are OK it's working well enough. I bought the AS5 very recently from a local computer parts store but who knows how long it was sitting around there for.

What alternative pastes would you recommend that are less thick?
Honestly, pastes make little difference in the grand scheme of things, as long as you don't get the awful cheap tacky stuff you'll be fine. Myself and some others answered a big post about it here: https://forums.tomshardware.com/threads/best-thermal-paste-for-cpu-and-gpu.3513745/
 
For a thin paste I like Prolimatech PK-2 which is available in huge 30g tubes. I've tried Arctic MX-2 and MX-4 which is cheap and also comes in big tubes, but found it deteriorates and requires repasting every two years which is a hassle.

Your AS5 is fine, just press down hard and move the heatsink around in a tiny circle until you feel metal-to-metal scraping. I don't think AS5 ever goes bad but it's so tacky that it's about the most difficult paste to clean!

You can probably tell I go through a lot of paste, and I can tell you that practical considerations like longevity and ease of application/cleaning are more important than performance. Most pastes only differ by a few degrees, and I'm inclined to believe the worst ones mostly tested that bad just because it was more difficult to get a good mount with those. The Prolimatech is a piece of cake because it is so thin is squishes perfectly every time.
 

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