Q: Is this normal temperature for a Mac Pro Late 2013?

I don't see anything unusual.

Using programs like that only cause needless concern. You should get rid of it.

All Macs incorporate hardware sensors that constantly monitor its internal parameters including temperature, and will reduce its performance as necessary to keep them within operating limitations. If it fails to do that, it will simply shut down on its own. Using third party hacks in an attempt to circumvent or improve upon those features is ill-advised, and could conceivably invalidate any remaining AppleCare warranty. You should specifically avoid anything that arbitrarily alters its fan speeds, since all that will do is draw in additional airborne contaminants needlessly.

If you're having operational problems with your Mac Pro, describe the symptoms. The operating temperatures reported by that app (if they are to be believed) are not a concern.

I'm seeing exactly the same effect. Depending on room temperature and connected
Thunderbolt devices I see everything from 73 degree Celsius ( room 19C, no ext TB device),

through 81 degree Celsius ( room 23C, 2 ext. SSDs and UAD OCTO via two different TB ports),

up to 86C and even more as room temperature increases further.

This is on a new 2016 MP6.1 6-Core, 32G RAM.

As an engineer with quite some IC design experience I find it a valid question whether
temperatures e.g.  above 90 degrees are still safe or not. A hot device in idle mode is very
different from a "burning" CPU under heavy load. And it worries me too ( at least a bit :-)).

Yes, but the chips can stand maximums of around 125ºC before they go through thermal shutdown. When you play games or watch movies then they run hot. This is less of a problem for concern in desktops or heavy laptops with larger cooling systems, but lighter laptops do hot have cooling systems with the capacity to cool as much so things do get hotter. It is better not to run them hot for long periods of time without letting them cool down. Today's laptops are not gaming machines. Be sure to keep yours cool by elevating the rear to allow better airflow under the computer. Avoid using it in hot rooms or areas not air conditioned during hot weather.

what application is providing those readings and how can you be sure they are accurate?

you should test the integrity of the system with the hardware test built into the system

Using Apple Hardware Test - Apple Support

if the system is new and exhibiting temperatures high enough that they are noticeable when using the system or going near it take it into the Apple Store nearest you for a diagnostic

> Yes, but the chips can stand maximums of around 125ºC before they go through thermal shutdown.

Thanks, theratter ! Can you point me to some official Apple or device maker documentation ? And was does "thermal shut down"
mean for a switch diode ? (e.g are you assuming the switch circuit is doing some sort of "thermal throttling"  in dependency
of the switch diode temps ?? )

BTW, the hot "PCI-E Switch Diode" device is observed on a Mac Pro 6.1 late-2013 ( i.e. last generation) - i.e. we are not talking of
laptop cooling issues. Also the hot device temperatures happen already in IDLE  mode - with almost zero activity on CPUs and
Thunderbolt bus ( e.g. with 2-3% system load).

To JimmyCMPIT: AHT reported no problems. The machine is under Apple Care. Yes, maybe I have
                         to take it to the Genius bar Just hoped I could get some official data regarding
                         the "safe" temperature range for this device. I somewhat trust the program because
                         it helped me find other issues in the past ( e.g. DDR2 RAM with badly sized RAM coolers in a MP3.1,

                         the machine much quieter, with lower fan speeds after replacing the RAM ...). But of course I do admit
                         that such SW could occasionally report irrelevant or false information - never mind ...