Intel 8700k suddenly one core hotter than all the rest

[Vivid Dream]

My i7 8700k is delidded with LM & has been comfortably running on 5.2 GHz 1.38v with temps of up to 65 degrees Celsius benching a score of 1670 on Cinebench R15 for a little over a year now. I did a random temp test using realtemp & Coretemp recently (after watching a de8auer YouTube video) while running Cinebench R15 & my core 3 temp spiked to 100 degrees while all other cores remained at 65 and lower & my pc locked up and I had to force shutdown. Then I restarted & ran it again & the same thing. I suspected maybe it was the thermal paste, so I cleaned it up, reapplied paste & reseated, but still exactly the same temps. The 100 degrees Celsius spike on core 3 happens instantly as soon as I hit Run on cinebench, before the fans have a chance to increase RPM, so I'm guessing it's the temp inside the package heating up so darn fast. So after that I then bought a new cooler, Noctua NH-D15. No change in temps across the board. My cooling us more than adequate, though for some reason all of a sudden my core 3 has decided to run extremely hot. Like 30+ degrees hotter than the other cores. 

I updated my bios to the latest version & no change occurs. I tried tinkering with my overclock & I discovered that the more volts I give the vcore the higher the temps on core 3 become, but the rest stay the same... Why does it seem like my core 3 is receiving more volts than the other 5 cores?

 

Is it possible for the LM to shift position on the die underneath the IHS? I believe LM doesn't degrade within 1 year... Do sensors become faulty randomly? Does the TIM degrade over time? 

 

If no other solution comes to mind, I will delid & relid again & replace new LM to the die, though if that doesn't work I am absolutely beyond ideas... 

 

Any thoughts?

 

I'm running:

Gigabyte Aorus Z370 Gaming 7 rev 1.0

i7 8700k

G.skill Trident Z 3600mhz 2x8gb (dual channel)

Seasonic Prime Ultra Titanium PSU

Noctua NH-D15

[porina]

I've had problems before when repasting after delid, where temps suddenly got much hotter after some months. However I've only had this with regular paste, not LM. The systems where I've applied LM still seem to work fine in long term. Still, if a core is getting hot, I'd suspect something has shifted and I'd focus efforts under the IHS than over it. Possibly uneven cooler mounting might cause problems, but the noctua system isn't bad at that.

[Vivid Dream]

Thanks for the reply. I've been scouring the web & YouTube for answers for days.. I will let you know what happens when I relid with LM again. 

[Mick Naughty]

Haven’t noticed anything like that on my older chip. Just did the 8700k a few days ago. 

 

Not watching all the cores on it but perhaps I should. 

 

I’d definitely take it apart and look. Shouldn’t be that hot without the delid so something had to have changed. 

 

Wouldnt assume sensor unless that margin remained at idle. 

[Vivid Dream]

Okay. Idle temps are more than fine, all 6 cores idle between 24-28 degrees Celsius, though as soon as I hit it with a chunky AVX workload like Cinebench R15 core 3 temps spike out of contr & my PC has a fit.

[porina]

4 minutes ago, Vivid Dream said:

Okay. Idle temps are more than fine, all 6 cores idle between 24-28 degrees Celsius, though as soon as I hit it with a chunky AVX workload like Cinebench R15 core 3 temps spike out of contr & my PC has a fit.

I don't think R15 uses AVX, but it is still a heavy load for non-AVX. Think they only added into R20.

[Vivid Dream]

I've had to dial back my overclock to 5.1ghz offer:1 just to keep my system stable. Very frustrating not knowing what has caused this change in performance.

[Vivid Dream]

Just now, porina said:

I don't think R15 uses AVX, but it is still a heavy load for non-AVX. Think they only added into R20.

Not sure, I read somewhere yesterday that it did. I'll check now to satisfy my curiosity.

[Vivid Dream]

4 minutes ago, porina said:

I don't think R15 uses AVX, but it is still a heavy load for non-AVX. Think they only added into R20.

Yeah it doesn't, thanks for that.

Oh well, still I never had these temps on this overclock; before now everything was peachy. Gonna have to take a look under the hood I think.

 

I've read about some cases where people's RAM sticks were causing temps to spike on individual cores, something about a memory controller in the CPU or something.. Also in another case, the guy replaced his PSU and it fixed the problem. It's so strange... Why can't things just be simple. Ugh, so many things that could be wrong. #isolationtesting #suchislife

[Falkentyne]

Did you make two topics asking the same question?
I replied to the other one =.=