In RD600 cpu throtlles @ 85c via smartguardian. Shutdown temp set in bios also reads same temp. this is not the same temp that Coretemp displays(61c).

So, unless it's the bios @ fault on RD600, Coretemp is not reading correctly. I have same issue too, reading 19c idle in 25c ambient, using AIRCOOLING.

this being said, coretemp reports same temp across many different boards for same cpu, when voltages/cooling are the same. Although the temp may not be perfectly accurate, it's the best we got ATM.