I put together a PC yesterday, which went smoothly up until I loaded up Open Hardware Monitor to check the temperatures of each core on the CPU.

The build used the following:

  • i7-8700k CPU
  • ASRock Z370 Extreme4 motherboard
  • Cryorig H7 CPU cooler with Arctic Silver 5 thermal compound

While cores 1-3 and 5-6 are reading low temperatures at rest - 25-26 degrees Celsius, core 4 is reading 108-109 degrees Celsius.

Core 4 is also under little to no load while reaching these temperatures. My BIOS also reports a CPU temperature of ~39.9 degrees Celsius, which is consistent with what I see in Open Hardware Monitor upon starting Windows.

I thought I may have applied the thermal compound incorrectly, so I removed the CPU cooler and remounted it, applying the compound in a different way (I spread it with a card the first time, this time I just put a small dollop in the center of the CPU's heat spreader and mounted the cooler facing the other way since I'd mounted it backward the first time), but the problem persists with almost exactly the same temperatures on all cores. The CPU cooler's fan is not increasing its speed despite the high temperature on core 4, either, though I'm not sure if it should.

After reading some answers, I've also tightened the screws on the cooler's backplate. There has been no change in the temperature readings.

What could be causing this, and where is the problem likely to be? What can I do to fix it?

  • Have you stress tested the system? Only way to determine if there is an actual problem
    – Ramhound
    Dec 2, 2017 at 4:35
  • I haven't. I'll run one and see how it goes. Dec 2, 2017 at 4:42
  • ~20 minutes into running Prime95 on default settings; CPU temperature rose to a maximum of 69 degrees Celsius. Core 4's temperature hasn't changed, while most of the other cores have risen at least a few degrees, with Core 1 rising about 10-15 degrees. All are at 100% load. Dec 2, 2017 at 5:10
  • 5
    Sounds like a bad sensor. Could be the CPU is bad. But it’s confusing to me about what you said about the BIOS saying 39.9 degrees and how that is consistent? How is that consistent with the 100+ degrees on core 4 and the 25 degrees for all other cores? Dec 2, 2017 at 5:45
  • I averaged all the core temperatures, and got about 39.9 degrees. I just did it again with the current temperatures, though, and it doesn't match up. The reported BIOS temperature is consistent with what I see in Open Hardware Monitor in Windows, though. Dec 2, 2017 at 5:52

1 Answer 1


It seems likely that the temperature being reported for core 4 is inaccurate. This could be due to a hardware problem or it could be due to a firmware or software issue. Since it doesn't seem to be affecting anything, I wouldn't worry about it. But, I have to admit, it would annoy me.

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