Mysteriously hot machine; Where to begin troubleshooting?

Mysteriously hot machine; Where to begin troubleshooting?

I'm running the latest Arch Linux on my ThinkPad t420 laptop, and am
having an intermittent heat problem where my temp will rise from the
typical ~50°C to ~75-90°C, and stay there until I reboot.
As I'm clearly no Linux guru, the extent of my knowledge for diagnosing
this issue pretty much ends with examining htop and CPU load, which is
minimal, load hovering around 0.1 and all processes using minimal CPU (and
all except htop, presumably (S)leeping).
sensors shows my fan buzzing along at ~3900 RPM.
Beyond this, I don't know where to begin troubleshooting, thus my problem.
I'm hoping someone could point me in the right direction to begin looking
for the deeper issue.



I did notice one seeming anomoly in my idle state report on powertop. Note
the high percentages of the C7 lines:
Package | Core | CPU 0 CPU 1
| | C0 active 3.0% 1.3%
| | POLL 0.0% 0.0 ms
0.0% 0.0 ms
| | C1E-SNB 1.5% 0.4 ms
0.2% 0.3 ms
C2 (pc2) 0.0% | |
C3 (pc3) 0.0% | C3 (cc3) 1.5% | C3-SNB 1.1% 0.8 ms
0.2% 0.6 ms
C6 (pc6) 0.0% | C6 (cc6) 0.0% | C6-SNB 0.0% 0.4 ms
0.0% 0.0 ms
C7 (pc7) 0.0% | C7 (cc7) 91.9% | C7-SNB 94.5% 3.3 ms
98.4% 5.5 ms
| Core | CPU 2 CPU 3
| | C0 active 2.5% 1.7%
| | POLL 0.0% 0.0 ms
0.0% 0.0 ms
| | C1E-SNB 0.4% 0.2 ms
0.1% 0.1 ms
| |
| C3 (cc3) 0.8% | C3-SNB 0.4% 0.7 ms
0.2% 0.7 ms
| C6 (cc6) 0.0% | C6-SNB 0.0% 0.8 ms
0.0% 0.0 ms
| C7 (cc7) 94.3% | C7-SNB 96.9% 5.3 ms
98.1% 6.4 ms
| GPU |
| |
| Powered On100.0% |
| RC6 0.0% |
| RC6p 0.0% |
| RC6pp 0.0% |
... Of course I don't know what these are percentages of and/or if they're
normal (just grasping at straws).