A8-6600k Temp Readings

Sounds like some bad temp sensors.

Yes you're just going to have to sort out what you are reading from where... I think part of your problem is software, and part of it is a misunderstanding of what sort of readings you should be getting in various places...

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Tips:

1. In BIOS, the CPU is NOT at idle. In fact, the BIOS creates a sort of dummy load for the CPU to keep it in the maximum power state under partial load. It's normal to see elevated CPU temps in BIOS.

2. As you are likely aware, the way AMD reports core temps is not based on a true accurate temperature, but is rather like a very precise relative reference. Some software may have built in algorithms that attempt to "correct" for this and produce a more realistic temperature reading (the actual junction temps are usually higher than the temp reported by AMD), this may or may not be what is going on with SIW. In my experience, lm-sensors in linux reports AMD PileDriver core temps in a way that works well, which is the precise but not necessarily accurate output on a scale where 70C coincides with 0 thermal margin, and 80C coincides with with the "critical/shutdown" temp for APUs, (90C for vishera on am3+). It's not unusual for this scale to report sub-ambient temps when the CPU is in low power states or under low to no load (again, precise, not accurate).

More than likely, there is NOTHING wrong with your hardware. Try more software to see what sort of results you get.. Boot from a linux live USB stick and see what it reports. (run "sensors-detect", then "sensors")

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There are lots of little tricks you can do to get more performance and lower temps from these APUs. At "Stock" settings CPB and turbo CPB are often enabled, which are technologies that override whatever VID the chip actually calls for at it's base clock, and can run (often) excessive voltage to run turbo speeds... These technologies apply a sort of "one-size-fits-all" voltage scaling profile for turbo speeds, which if often higher than required. There are lots of ways to "fix" these inefficiencies and even tweak some additional performance out of these chips, however, it all falls under the umbrella of custom performance tuning (over/under-clocking, custom voltage, etc).

If you're interested in some pointers to get the most performance out of that APU with custom performance and voltage configuration let me know.

It's my "expert" opinion that there is nothing wrong with your hardware based on the information given thus far. Your temps in BIOS sound about right for the boxed AMD cooler with all factory settings on the board. The 6600K is going to run close to it's thermal margins at factory settings with the stock cooler when under a load, this is just the nature of the beast here (very little dissipation headroom here).

I think it would be a good idea to monitor AMD's software or try some other software like CPUID's HWmonitor and just make sure that your peak temps are not exceeding the "thermal margin" while under a load. I would personally want the machine to have at least 5-10 degrees of headroom to the maximum recommended operating temps with a clean newly installed HSF while running Prime95 + Furmark simultaneously. Achieving this sort of headroom may require changes to both the configuration (voltage, power management, fan management, etc), and the cooling performance of the system. The CM212 EVO is very popular, and a good performer, but unless you're planning to push for a nice overclock, you can actually get by with smaller, easier to install coolers like the Arctic A11, SilverStone AR02, or Zalman CNPS5X.

I also like the SilverStone AR06 for "OE" upgrades, as it provides good VRM cooling, though it's more expensive.

Installing an aftermarket cooler is entirely optional, you can get the same headroom by tuning the operating speed/voltage of the APU to better match the thermal solution in place. Simply disabling Turbo CPB and CPB can cut power dissipation by up to 25%.