Uneven Core Temp on i7-4790K

[Bike4]

I have an i7-4790K (not overclocked) with a Noctua NH-U14S cooler. The fan is PWM under BIOS control (silent profile). At idle all 4 cores are around 42°C. At full load I get a bit of disparity. The cores would be 64, 68, 74, 69. I was wondering if that’s normal or I’ve done a bad job applying thermal paste?

The second question is this: I run Prime95 for a few minutes and everything’s fine (CPU temp around 70°C). Them, all of a sudden, it’d shoot to over 85°C at which point I’d promptly shut down the system (it seems that closing Prime95 does not immediately reduce the CPU load). I repeated the process twice with the same results. Then I switched the fan profile from silent to turbo. The CPU temp was running a little cooler this time (high 60s), but then after a few minutes it again shot to over 85. Is that normal? What's going on here?

Thanks!

 

[Baralis]

The core temp variance is normal and a person can reasonably expect to see up to a 10C range at load. Manufacturing, construction, and sensors are imperfect hence the differences.

Newer versions of prime95 use AVX instructions as part of their stress environment. This causes Haswell's to apply a higher voltage and greater heat. It is not recommended to use above prime95 version 26.6 on a Haswell chip.

 

[sportsfanboy]

It is normal to vary in core temps. The main reason is the sloppy uneven method used to apply thermal interface material to the chip underneath the heat spreader.

 

[Bike4]

Thank you guys!

I've updated my BIOS, apparently the new version has improvements to the CPU fan. I've also downloaded Prime95 26.6. Everything's fine now, CPU temp doesn't go over 70.