CPU goes to 100 deg coming out of standby
Within the past year, I replaced the original drive with a 512 Gb Fusion drive from iFixit. I also replaced the CDROM with an SSD drive. I don't have a reason to believe this is causing my problem but it is worth mentioning.
When I look at my CPU temp with iStat right after coming out of standby, it is 38 C. Within 5 min, if I do nothing, it is up to 100 C, and Heatsink B is 78 C. Fan is maxed out at 6200 RPM. It then settles down to something like 91 C / 75 C. Room is cool and laptop is on a hard surface and well ventilated externally. These numbers are obtained running as a laptop, but the same kind of thing happens in closed-clamshell mode with an external display. In fact, in closed-clamshell mode I have had some "You need to reboot your computer" conditions, which I'm guessing are due to overheating.
Some things to consider (from other postings) seem to be:
1. Run the hardware test.
2. Check for fan obstruction or dirt. (The fan sounds good -- nice, even white noise; not too loud.)
3. Replace heat-sink compound.
Is that the best sequence to try? The disparity between CPU temperature and heat-sink temperature leads me to suspect (3), but I don't know what normal is.
Also, I have about 10 browser tabs normally open in 2 chrome windows, but I have flash disabled. Activity Manager and top show low activity with a load factor of 0.23. It may briefly peak for a few seconds after coming out of standby, but still, I can't connect the high temp to anything I'm doing under these conditions. No vidio streaming, no games, no great CPU or graphical load.
For a while I disabled the kernel_task kext that was taking up CPU, but have re-enabled it and see it running from time to time.
Advice as to next step(s) would be appreciated.