4790k CPU suddenly running very hot without changes

Jun 11, 2015
Gigabyte GA-Z97X-UD3H-BK
5700 XT
  1. MacBook Pro
  2. Mac Pro
Classic Mac
  1. Power Mac
Mobile Phone
  1. Android
The Coles Notes:
My CPU temperature has suddenly jumped from 72c to 99c at load.

The details:
Nothing has changed in my setup or BIOS! I’ve got the following system specs:

4790K running at 4.3ghz
Cooler: Phanteks PH-TC14PE
Motherboard: Gigabyte GA-Z97X-UD3H-BK
RAM: 16GB Kingston HyperX Fury White 1866mhz
PSU: Seasonic X650
Case: Fractal Design Define R4 with Window
GPU: Asus GTX 980 Strix

I’m running Mac OS on an SSD and sometimes do a bit of gaming in Windows on a 1TB WD HDD (mostly BF1). Idle temperature is very low at a comfortable 29-32c. Ambient temperature in my room is typically around 18-22c.

I very frequently run Handbrake in Mac OS to compress video files… typically 2-3hrs per day or sometimes 10hrs straight. At this point, the CPU cores are all being worked at max. I’ve had the system for 3 years now and last week after a couple hours of gaming in BF1, I noticed the case was warm to the touch.

I booted up Mac OS to do some file compressions and the CPU temps spiked well beyond 80c, then 90c and eventually peaked at 99/100c, never going past that.

I tried re-applying the thermal paste (Arctic Silver 5) using the grain of rice method and my temps remained the same.

I noticed the CPU voltage was peaking at 1.3v under load, so I decided to change the voltage settings from AUTO to 1.5v. That helped, but not a whole lot. Instead, I got about 90-95c temperatures.

I dropped the voltage down to 1.2v and my temps went down to about 70-80c BUT after about 30-60 minutes of running Hanbrake, the computer just rebooted on it’s own.

I thought perhaps the CPU isn’t getting enough power so I increased the voltage up to 1.23v however the temperatures are really wonky. They start off ‘low’ at around 65-70c, then rise slowly to 75c. After about 30-45 minutes, it increases to about 85c… but it has moments where it will dip down to 79c and shoot back up up to 88c and then stay there.. hit 90, then drop down to 65 and shoot back up to 85c.

I tried loading optimized defaults in the BIOS, with the CPU set to 4ghz stock. Only change I made was disabling the integrated GPU on the chip and disabling VT-D. Temps went right back to 90c and up. After this I re-applied the thermal paste using the spread method, after about 15+ minutes of stress testing in Handbrake, the temps are typically between 85-88c but can jump to 90c and down to 75c. At around 30 minutes, it's running closer to 91c... and then 92c.. dips down to 79c again, back to 90...91..88...90...92...

A bit more tinkering around and it seems that for a 10 minute stress test with 4.0ghz stock speed keeps the CPU at 65-70c.

What is going on?


It's really embarrassing; after cleaning out my fans and inside of the case from dust buildup a few weeks ago, I put in the exhaust fan BACKWARDS which resulted in the interior of the case turning into an oven over time. Pathetic, I know but I've got my temps down finally and all's back to normal. I guess it explains why after an extended period of time, the whole system gradually got warmer and warmer as the heat had nowhere to go. THANK GOD for iStat Menus!
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