I've got a Mac Pro (early 2009) that I upgraded with an Intel Xeon W3690 (3.46 GHz) a couple years ago. Of course it has the MacPro5,1 firmware as well. It's been absolutely rock solid, but ever since upgrading to Sierra, the fans quickly go out of control for no apparent reason. Temps are more than reasonable, ranging from around 71°F ambient and DIMM temps to a max of 96°F at the power supply. CPU temp (heat sink, diode) is around 85°F (CPU core is about 75°F). The PCI and PS fans are fine, but the exhaust, intake and Boost A fans are running at full speed non-stop. I'm attaching a screenshot that shows the fan speeds and temps, and you can see that exhaust, intake and Boost A are maxed out when left to their own devices:
I have thoroughly cleaned the case and fans of any dust and debris. I have repeatedly reset the SMC. On restart the fans are fine, but then for no reason those three will eventually jump to full speed again even when temps are fine and there's no load, and they don't slow down unless forced (e.g. with Macs Fan Control) or the computer is rebooted (lather, rinse, repeat). Computer has all of the latest OS updates, and no processes are running amok.
Any thoughts? Again, this only happened after the Sierra update. I searched but haven't found similar reports, and I can't imagine Apple is going to be too helpful with a 2009 Frankenstein machine (unless I wanted to pay through the nose for support). Obviously I can force the lower fan speeds with Macs Fan Control, but I'd rather solve the problem. I guess I'm wondering what specifically tells the computer to make these fans go faster.
Barring a real fix, suggestions on temp ranges (especially max) and which sensor(s) to use to use sensor-based control for the affected fans via Macs Fan Control would be much appreciated.
Thanks in advance,