Thanks very much @DanielCoffey for posting this great guide. I found it via Google when planning to do the same task myself on my various LSI controllers.
It was very helpful to see in advance what I would experience, particularly as this was the first time I'd replaced a heatsink on a PCIe card, so I'd never before seen or dealt with the 'arrow-head' pins. And it was very useful to know that the heatsink wouldn't simply come away from the chip and needed prising. These sticky pads that LSI use are a bit of a pain!
I also wanted to comment on this. While I absolutely agree that it's worthwhile to refresh old paste, I'm not sure if this method of testing the before/after is accurate or useful. And I'm worried that the figures you posted could actually mean the opposite of what you hoped.
Here's my thought process. The temperature on the heatsink is a factor of two things: 1) the amount of heat transferred from the chip through the paste; 2) the amount of heat dissipating from the heatsink into the air. By changing the thermal paste we affected 1, but we did not affect 2. By improving the thermal conductivity, arguably we are more likely to see higher temperatures on the heat sink. Better paste means more heat sucked out of the chip, and as we haven't improved the airflow/cooling, that should result in the same or even a higher temperature on the heatsink. Which is OK, it's the chip temperature we want low.
The dissipation from the heatsink depends on the size/structure of the heatsink and the amount of airflow over it, which together give us a heat dissipation rate (degrees C per second or whatever. ) This dissipation rate is then also affected by temperature - hot objects dissipate heat faster then colder objects - but I don't think this effect would have a material difference in this case (I think it balances out because the chip itself is also cooler).) Especially with only a few degrees of difference.
Therefore I'm pretty sure that we can consider the dissipation rate constant before and after the thermal paste change. The only thing that changes is the greater rate of heat transfer from the chip through the paste. Therefore if anything we might expect a rise in heatsink temperature. The chip itself will experience a drop - our real goal - but as we can't measure that, we wouldn't see it.
So I'm worried that your measurement of a lower heatsink temp could actually mean that the new thermal paste is performing worse: you didn't change the airflow, and therefore you didn't affect the heatsink's heat dissipation rate to any significant degree, so a lower temp on the heatsink seems to imply less heat being transferred from the chip and therefore a higher temperature in the chip. Which could only be caused by lower thermal conductivity between chip and heatsink.
I'm quite possibly missing something here, but that's how it seemed to me. I'm certainly not a physicist so do let me know if there's any flaws in my logic, assumption or facts! In fact I debated whether to post this, as it was a great guide and I didn't want to rain on your parade by potentially indicating it has had the opposite effect. But I'm still hoping I might be wrong and that someone will correct me.
Even if I'm not and you have had a bad result, it gives the opportunity to try again; the method certainly should work and is definitely a good idea, especially using enthusiast quality thermal paste that should outperform any standard stuff. So it could be that something just went wrong on your attempt. These heatsinks cam be a bugger to get back on, mine took me two attempts because the first time I couldn't get the heatsink back on properly and I was smearing paste all over the place. So I stopped, re-cleaned, and did it cleaner the second time.
Needless to say that because of the above thoughts, I didn't bother testing the before/after temp of my heatsinks when I did my thermal paste refreshes. In the absence of a chip temperature sensor, and with the worry that it can only show a worsening of heat transfer, I'm just going to assume it's worked OK
Thanks again for the great guide.