[SOLVED] Ludicrously high idle CPU temperatures?

[Leoki]

I have a bit of an issue troubleshooting this CPU temperature issue. About a month ago, my 4-year old PC started to hard hang that required a manual reset, and eventually, it started auto-shutting off. Now, the PC auto-shutoff with about 3-5 mins of normal use. The symptoms seemed to point towards overheating, so when I rebooted I went into the BIOS, and lo & behold, the BIOS was giving a CPU reading of 86C and climbing, auto-shutting off at 90C. So I replaced the thermal paste and let it sit overnight. The following morning I booted into BIOS again and it was reading 56C right off the bat. It rose up to 76C~80C within ~3ish mins and just idles there, even with all the case panels open. I still can't get 5 mins of use out of it before it shuts down.

I originally thought it was 1 of 3 issues: PSU failure, cooling failure, or faulty temperature sensor. However, I can rule out the PSU because I replaced it, and the problem still persists. Out of cooling failure and faulty temperature sensors, I'm leaning towards the sensor. BIOS puts the cooler pump rpm at 2200 and the exhaust air coming from the radiator is relatively cool, certainly not 80C hot. Additionally, I confirmed the pump is indeed running using a stethoscope and there is circulation as one of the hoses is hot and the other is cool. Also, a temperature gun reads 35C when pointed at the back of the socket and surrounding motherboard. However, all my research says that sensor failure is pretty rare and coolers die much faster. Also, many say that although the pump may be running/ it still may be faulty.

Honestly, I'm at a loss and really need some more opinions. Is it the cooler or the sensor? Which part do I replace if it's the sensor? Is there anything else that may be at fault?

Specs:
cpu - AMD FX-8350
mobo - MSI 970 gaming
cooler - Corsair H100i GTX
psu - EVGA 600W (was corsair HX750i)

 

[carocuore]

BIOS puts the cooler pump rpm at 2200 and the exhaust air coming from the radiator is relatively cool, certainly not 80C hot. Additionally, I confirmed the pump is indeed running using a stethoscope and there is circulation as one of the hoses is hot and the other is cool.

If it's 4 years old it's possible the pump still works but the cooler is clogged somewhere, probably in the radiator, or that there isn't enough liquid to circulate through the whole loop, if one of the tubes is hot while the other is cold and the fan blows fresh air through the radiator then something's not working.
Both of the tubes should be at least warm, and the fan should blow warm air, also, a CPU sensor fault is very unlikely, and if it failed it wouldn't report high temperatures, it'd report nothing, in fact.

It's also possible that the AIO speed sensor reports a working pump even though the impeller is stuck.
Again if it's a 4 year old AIO then it's probably its time to go had come already. Do you have any air cooler to try? Those FX came with an stock solution, try that if you still have it.