athcool is .. cool! The new server mainboard was consuming some more power and was at a higher temperature. I looked for ways to reduce this a bit. Setting power throttling mode to T1 did not help for power use or temperature (but the system reacted slowish), but athcool made the readouts from lm_sensors change from CPU Temp: +42.8 C to CPU Temp: +21.5 C which looks a lot better. And, more important: the UPS reports a drop in power-use, which is good for the electricity bill. Follow the graphs at my assorted sensors at home.
Update: the chance of instability mentioned in the documentation happened to me so athcool is disabled again on the server.