Cooler master gemini II S + i5 = headache

Greetings experts,

I'm hoping someone with some experience with installing heatsinks can help me here.

I am trying to install a cooler master gemini II S aftermarket heatsink onto an i5 processor using arctic silver 5 thermal paste in an antec fusion black case.

Following the directions on the arctic silver website to the letter, I painted a thin line of thermal paste down the center of the processor, installed the heatsink per their directions, and used Prime95 (max CPU load/heat) to test for temperature.

I am idling at 36-38c and as soon as I turn on prime95, in under a minute or two I am running +60c (via Coretemp and PC-probe II). At this point, PC-probe tells me things are getting too hot.

No matter how many times I repeat this process or change how I am installing (more thermal paste, less thermal paste, tightening the heatsink more/less) I can not get it to work. I clean both the CPU and heatsink with 70% iso alcohol on a coffee filter each time.

As far as I can tell, the surfaces of the processor and the heatsink are flat. Although, each time I pull them apart to try again, I notice that the thermal paste is pushed to the sides with a "bald spot" in the middle where you are supposed to put the thermal paste to begin with since that is where the cores are. This happens regardless if I tighten the heatsink down hard or barely at all.

I have read numerous FAQs, the arctic silver 5 website, used youtube, and read anything google would pull up and I'm flipping stumped.

I'd appreciate any suggestions or advice.



EDIT: I just tried using the stock cooler that came with the i5, and my idle temps were 40c and I was +60c in seconds with prime95. augh...
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  1. Hmm, well that is to high as the gemini II is a massive cooler (that is the one with two large fans yes?) and you're getting the same results with the stock. Unless you've got the single fan cooler - in which case your temps are probably about right.

    When you say a 'bald spot' do you mean a lot of the paste has been moved, or do you mean it's completely gone (which i've never seen happen before and would suggest your cooler or CPU isn't flat). You can test if they are flat with a straight knife or razor blade. Normally when you pull a heatsink off the paste sticks to either the heatsink or CPU more, so sometimes it looks like it's bald but it's actually on the other component.

    Using more or less paste is more of a preference as I've tested my CPU with very little paste, and then loads.. and the difference was like 2C. Makes very little difference with high-quality paste. It might make more of a difference with the white crappy stuff that comes with heatsinks today.

    I would always say to tighten the cooler as much as you can (without breaking anything or putting too much stress on the retention system) because you want the cooler to be as close to the CPU as you can. Idlely (in terms of cooling) CPU's would have a massive heatsink and heatpipes connected directly to the chip(s) and stop the need for a layer of paste between the heat source and the cooler.

    If you've reset the cooler several times, I can't think you're doing a bad job.. but what kind of airflow do you have in your case? A cooler can only ever cool to the ambient temps in your case, so if you have 3 graphics cards and a million HDD's your CPU will run pretty hot as your motherboard, cooler etc.. all work at a higher temp.

    Last point.. Arctic Silver 5 takes 200+ hours of use before it's 100% set and gives best results. Normally results will only change by a few degrees, but it's something to keep in mind.

    Let me know what cooler you have as I can't remember if yours is the two-fan cooler I'm thinking of. And give some details about what case your using :].
  2. Thanks for the reply acer0169.

    The gemini II has one 120mm fan on it. It comes with rails to set up two 92 mm fans, but they were not included.

    When I say bald spot, I mean that when I pull the heatsink away from the CPU both the CPU and the copper on the heatsink look as if the paste has been pushed to the sides.

    Here is a picture of the CPU after attempt #11:

    You can see that there is the least amount of paste right down the middle, where arctic silver says the paste needs to go the most since that is where the processor is. Does that mean I am getting a super-tight seal against the heatsink and as a result it is pushing the paste to the sides? Does that mean the CPU or heatsink is rounded slightly in the center? I used the edge of a piece of paper to test if the processor/heatsink were flat and both seemed okay.

    The antec fusion black case is a micro ATX HTPC-based unit. IT has 2 120mm exhaust fans that are set to high. I'm running a EVGA gts 250 for video, and a single 600 gig 7200 rpm western digital hard drive, so their might be some heat, but not so much that I thought it would be oppressive.

    At this point, I'm wondering if I screwed myself by remounting it so many times. The copper on the heatsink has a bunch of light scratches on it and the arctic silver website says that might decrease cooling efficiency. I'm really grasping at straws at this point.
  3. Okay.. right off the bat I'd say to use more paste. Instead of just putting a bead in the middle of your CPU, use a credit card or something similar to spread a thin layer all over the CPU so it's completely covered, this way where ever the heatsink touches the CPU, it's 100% going to have paste between it.

    Scratches on your heatsink shouldn't make much of a difference (even a cooler in a poor state might only lose one or two degrees because of scratches).

    Does your case have an intake fan? Or room to mount a 120mm / 92mm fan on the inside somewhere to push some more air towards the CPU? On my Cosmos S, I have a fan mounted where optical drives should go as this helps push air to my cooler and this has dropped temps by 5C.

    Because it's a HTPC unit with a warm GPU (the 200 series are all pretty warm) and (maybe) no intake fan, I'm not too surprised at your temps. They might be a little high, but that might be because the fan on your CPU cooler hasn't got much room to draw cool air.

    Remount using more paste and spreading it manually before putting the cooler on. Then report back if it's made any difference.

    I'm watching this thread so I'll continue to help until you're happy with your new cooler.
  4. I tried using the plastic baggy method once (finger in plastic bag, smear thin coat of AC5 over entire processor) but didn't see any difference in temp.

    The case does not have an intake fan, nor a place to put one. After reading your reply, I kludged a solution by using an antec "spot cooler" fan set to high. I positioned the fan over the large mesh intake in the rear of the computer and aimed it so the cool air would hit the heatsink directly.

    From what I can tell, adding the intake fan helped a bit. I was able to keep prime 95 (large fft's) on for 10 minutes with the temperatures getting up to 62c (via Pc-probe) and 57c (via coretemp). The cores quickly rose to 55 degrees (via coretemp), then gained another 2 degrees but seemed to level off for the remainder of the time I was running it. Admittedly, I don't know if keeping prime95 on for an hour would make the temp slowly climb into a danger zone, but how realistic is that as a test to run the max heat setting on prime95 for that long? What program would tax a CPU at 100% on all 4 cores for an hour straight?

    I'm never overclocking this system, so perhaps I am at a reasonable level at this point?

    I really appreciate the support acer0169; you're a class act.
  5. Keeping prime95 running for an hour would be a perfectly fine test. It's good for stability, but also very good to see what your max temps are. Once your temps have leveled off, the only thing that would make them slowly rise would be if your ambient case temp also goes up.. but with a good exhaust fan (or two) you should be fine.

    I think I've read the safe temps for a i5 is around 80C, so as long as you're not hitting that.. you're fine really.

    Maybe with hindsight a slightly bigger cooler would have been a good move, or one with a second fan attached, but that's always easier to say once you've bought and tested one properly ;].

    If you're not overclocking the system, even if it's a little warm; I think you're okay. It's stable, not too hot and will never burn out as your temps seem about the same as what others are getting with mild overclocking.

    If you had a large intake fan you'd see quite a difference, so maybe down the line you could get a new case or something?

    Support is my thing ;], you're welcome mate.

    Dunno if this goes against any TH rules but feel free to email my directly at questions[at] if you have any further questions :].
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