K5-PRO Viscous Thermal Paste vs Gelid GP-EXTREME Thermal Pads on the Gigabyte AORUS GeForce RTX 3090 XTREME

In this article I will be looking at how K5-PRO Viscous Thermal Paste, which was recently highlighted in a recent video by Linus Tech Tips, compares to Gelid GP-EXTREME thermal pads on the Gigabyte AORUS GeForce RTX 3090 XTREME.

Despite the enormous (nearly 4-slot) cooler, this is one of the worst performing air cooled RTX 3090 cards on the market — with stock thermal pads and stock thermal paste, would hit over 100c on the GDDR6X Junction and the GPU hotspot would peak at around 90-95c depending on the game, with fans at 100%

RTX 3090 FTW3 (left), RTX 3090 AORUS XTREME (middle), RTX 3090 FE( right)

I had already swapped out the thermal pads on this Gigabyte RTX 3090 AORUS XTREME card for Gelid GP-Extreme thermal pads, for which I used 2mm thick pads for the VRAM (front and back) and replaced the Mosfet thermal pads with 1.5mm pads, all other pads were stock.

Once I saw Linus's video I ordered a tub of K5-PRO to test it out, see how it performs and if you should buy it.

How K5-Pro compares to Gelid GP-Extreme pads

K5 Pro is advertised as having a thermal conductivity rating of 5.3W/mK, can be heated up-to 250c, is suitable for replacing pads up-to 3mm thick and has a "practically infinite" lifetime, according to the Amazon listing page.

Gelid GP-Extreme is advertised as having a thermal conductivity rating of 12W/mK and comes in 0.5mm, 1mm, 1.5mm, 2mm and 3mm thicknesses, with a hardness rating of 35 OO Shore.

Looking purely at these advertised numbers, you would assume Gelid GP-Extreme would be the better performer, so why would you bother with K5 Pro?

The short answer to that is choosing the right thermal pad, especially for a high end graphics card like an RTX 3070 Ti, RTX 3080, RTX 3080 Ti or RTX 3090 can be tricky. 

You have to choose a thermal pad that is the right size, right thickness and compresses the right amount, if your pad is too thin, it won't make good contact with the VRAM or Mosfets and as a result you may get hotter temperatures than simply sticking with the stock thermal pads. This can be especially tricky as most thermal pads at retail are sold in thicknesses of 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm and 3mm, whereas some GPUs require pads that are 1.25mm, 1.4mm, 1.6mm, 1.8mm etc...

Likewise if the thermal pad is too thick or doesn't compress well enough, you may get really good VRAM and Mosfet temps, but get really poor GPU or GPU hotspot temps if the GPU die doesn't have enough mounting pressure.

K5 Pro being a viscous thermal paste, suitable as a thermal pad replacement should in theory better fill the gaps between the heat source and heatsink, without the need to worry about having a thermal pad which is the right thickness or hardness rating.

Results with Gelid GP-Extreme Pads

To test how the card already performed with Gelid GP-Extreme pads, we used FurMark 1.29 at 2560x1440 with 8x MSAA and within FurMark's options, we had Dynamic Background, Burn-in, Xtreme burn-in and Post-FX enabled to give us a worst-case scenario for GPU thermals.

Here are the results

After running the test for over 45 minutes, our GPU temperature peaked at 74.3c, our GDDR6X junction temperature peaked at 92c and our GPU hotspot peaked at 92.4c. The ambient temperature was 22c when this run was conducted.

This is an improvement over the stock thermal pads and paste, but still very poor considering the size of the cooler.

Applying K5-Pro

Our next step is to disassemble the GPU and apply K5-Pro, the GPU die, GDDR6X memory and Mosfets were cleaned with 99.9% Isopropyl alcohol and a thick layer of K5-Pro was applied to the GDDR6X modules, Mosfets and VRMs. For the GPU die, Arctic MX-5 was used.

Here's the application on the back of the PCB

Here's the application on the front of the PCB

Time to put the card back together and run the same test again

Results with K5-Pro

To test how the card performed with K5-Pro, we used FurMark 1.29 at 2560x1440 with 8x MSAA and within FurMark's options, we had Dynamic Background, Burn-in, Xtreme burn-in and Post-FX enabled to give us a worst-case scenario for GPU thermals; the exact same settings as before.

After running the test for over 45 minutes, our GPU temperature peaked at 60.4c, our GDDR6X junction temperature peaked at 112cc and our GPU hotspot peaked at 71.4c. The ambient temperature was also 22c when this run was conducted.

Here's a comparison of the two runs

Gelid GP-Extreme

GPU Temp: 74.3

GDDR6X Temp: 92c

GPU HotSpot: 92.4c

K5-Pro

GPU Temp: 60.4c

GDDR6X Temp: 112c

GPU HotSpot: 71.8c

These results were about where I expected them to land, our GDDR6X junction temperature was 20c hotter with K5 Pro compared with Gelid GP-Extreme pads and exceeded the 110c at which the card will throttle, on the plus side our GPU hotspot went down by 20.6c.

I think this is quite significant, I had always assumed the reason the RTX 3090 AORUS XTREME performs so bad thermally was because unlike most other RTX 30 GPUs, it didn't use a leaf-spring, so not enough pressure was being applied to the GPU die, resulting in poor contact and high hotspots.

After doing this test, it shows that this cooler is actually more than capable of cooling the card, despite not having a leaf-spring but that even the stock thermal pads Gigabyte include are too thick and end up causing issues with GPU die mounting pressure.

Conclusion

In conclusion I can say that if you are wondering whether K5 Pro is worth it over regular thermal pads for an RTX GPU with GDDR6X memory, I would say avoid it, going with quality thermal pads from Gelid, Thermalright or Thermal Grizzly will give you much better results and will be way easier to apply and clean up, should you ever disassemble the card again.

K5 Pro may be better suited for lower-powered devices, like games consoles, laptops, motherboard heatsinks and even GPUs with regular GDDR6 or GDDR5, which run much cooler than GDDR6X, but that is simply outside the scope of this short article.

I hope you found this article interesting or helpful

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Follow-up, some further questions and recommendation against K5-Pro

A day later and this this post has been posted to /r/hardware and /r/nvidia, with some questions in the comments, which I will now answer

/u/VenditatioDelendaEst from /r/hardware writes

This is kind of left as an exercise to the reader, but it's almost certain that reason the GPU hotspot temperature went down is that the card is throttling. I didn't find a link to any previous article about how these results compare to the factory original thermal interface.

This is a good point that wasn't addressed in the article, and I don't believe the reduction in the GPU hotspot temperature is down to the fact the card throttled. With the Gelid GP-Extreme pads, the card averaged 417W, whereas with K5-Pro, the card averaged 370W.

I can confirm that before doing this article, I did try reducing the power limit of the card all the way down to 85% (around 355W) in MSI Afterburner and it had minimal impact on the GPU hotspot temperature, leading me to believe the high GPU hotspot temperature on this GPU with the stock thermal pads and Gelid GP-Extreme pads is down to GPU die mounting pressure.

/u/falkentyne from /r/nvidia writes

So in that article, that person clearly used the wrong thickness thermal pads on something, as the hotspot to core temp delta is atrocious with the Gelid pads, and the GPU core temp is much higher.

Yes, this is discussed in the article, the 2mm Gelid GP-Extreme pads are too thick, and the stock thermal pads that came with the card are also too thick and resulted in a GPU hotspot of 90-95c. 

A highly compressible 2mm pad or 1.7 - 1.8mm pad would probably work best here, but the latter is not readily at retail for consumers.

Cleaning up K5-Pro

For the final point, I can say that cleaning up K5-Pro is an absolute nightmare, I spent around 2-3 hours soaking the PCB in 99.9% IPA with a toothbrush, trying to remove the residue. I got it looking alright, but you can still see some of the K5-Pro left between the SMDs, capacitors and under the GPU die and GDDR6X modules.

I will let this dry for 12-24 hours and hopefully this card still works.