New build CPU temperature advice (AIO cooler, testing with Prime95)

Hi all, looking for a bit of advice regarding CPU temps.

So this is my first time building a PC from scratch - I've got it all up and running, and am now in the benchmarking/stability testing stage. Been running Prime95 to check CPU temps and am a bit concerned that my core temps are hotter than I expected under load.

For reference, I'm running an i7-6700k at stock speed (reported clock speed is 4.21MHz) with a Corsair H115i cooler (AIO with 280mm rad) installed with the pre-applied thermal paste + 2 fans in push mounted in the top of a NZXT H440 case (case also has 4 other case fans, 3 x 120mm pull at the front and 1x140mm push at the back).

Using HWMonitor to monitor temps, ambient temperature is about 25C and CPU core idle temps are 26-28C (so that seems decent).

Core temps under 100% load using Prime95 (each running for at least 10 mins):
Prime95 v26.6 blend - 69C max (average 64C)
Prime95 v26.6 small FFT - 73C max (average 69C)

Prime95 v28.9 blend - 82C max (lots of temp variation)
Prime95 v28.9 small FFT - 83C max (average 80C)

I actually ran the latest version of Prime95 first (and was seriously worried I'd totally messed up fitting the heat sink) - having read around, I gather that the latest version Prime95 does cause your CPU to run unusually hot and that v26.6 is the one to use, but I guess I still expected better results with the H115i cooler, especially since I plan to have a go with overclocking in the near future. Am I being unrealistic about how cool it should be running? Are these temps reasonable for Prime95? Or should I taking the whole thing apart and reseating the heat sink? (Slightly loathe to do that as I gather that the pre-applied thermal compound is supposed to be quality stuff and I haven't had to apply thermal paste myself before)...

Any help appreciated!
3 answers Last reply Best Answer
More about build cpu temperature advice aio cooler testing prime95
  1. Zaxian,

    Welcome to Tom's!

    At the top of this Forum (CPU's) you will see "Stickies" which are a group of Guides or informative Threads that are permanently available for everyone's reference. Within this group you will see one called Intel Temperature Guide -

    The information you seek is in that Guide, so please give it a read.


    CT :sol:
  2. Hi CT,

    Thanks for the response. I had actually spotted and read that thread prior to posting but didn't feel like it answered my question - but perhaps I didn't phrase the question very well.

    Essentially, according to that thread, 70C is a *safe* running temperature for a 6th gen i7 at 100% load using Prime95 v26.6. However, I guess what I was really asking is: is 70C an *expected* temperature, given that I am only running it at stock speed and *particularly* given that I have installed a high-end AIO water cooler? Or is it indicative that, for example, I have not installed the heatsink as well as I could?

    And should I be concerned that the temperatures push up to 80C using the later version of Prime95 (even though it's still '100% load' - I am aware that the later versions of Prime run hotter but 10C seems like a big jump)?
  3. Best answer

    The difference on some overclocked processors is as much as 20C!

    100% usage doesn't mean 100% workload.

    From the Guide:

    "Prime95 Version 26.6 Small FFT's is the standard for CPU thermal testing, because it's a steady-state 100% workload which runs Core 2 processors and Core i variants with Hyperthreading within 3% TDP at stock settings."

    This means that thermal testing with P95 v26.6 Small FFT's is as close as you get to replicating Intel's Thermal Design Power (TDP) specification. There are no other test softwares that I'm aware of which will so precisely peg the TDP spec.

    Although there are many excellent softwares for stability testing, this is why P95 v26.6 remains the best software choice for thermal testing.

    (1) Are your BIOS settings in "Auto"?
    (2) What is your Vcore during Small FFT's?

    Without knowing these variables, we can't say with any certainty what your "expected" core temperatures should be, and your water block seating concern is also another variable.

    High Vcore would help to explain your core temperatures. Also, to put it a little more into perspective, remember to take into consideration that if your ambient is 25C, then at 22C which is "standard" or "normal" ambient, your core temperatures would be 3C lower.

    Did you read this part of the Guide? ...

    "Core i 6th Generation processors have features such as Configurable TDP (cTDP) and Scenario Design Power (SDP) which may invoke throttling as low as 80C."

    Or this? ...

    "Core i 2nd through 6th Generation CPU's have AVX (Advanced Vector Extension) instruction sets. Recent versions of Prime95 such as 28.9 run AVX code on the Floating Point Unit (FPU) math coprocessor, which produces unrealistically high temperatures."

    Or this? ...

    "If you’re overclocked and run AVX apps, you may need to reduce Vcore and clock speed and / or upgrade your cooling so that Core temperatures don’t exceed 80C."

    If you're not using AVX software, then don't use P95 v28.9. You only need to concern yourself with your thermal baseline core temperatures during P95 v26.6 Small FFT's.

    CT :sol:
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