Coretemp also shows a value for Tj max. What is it for your processors? Coretemp can be set to show the difference between Tj max and the core temps. This temperature varies depending on the processor.
The CPUs will run hot when stressed, this is done on purpose to get maximum performance. I have run systems at 100% CPU load for weeks at a time, on multiple systems, and the max core temp was about 10 deg. C (or more) below Tj max.
If your CPUs are running closer to Tj max, some things might help to lower temps. Get the dust out of the case and heatsinks. Are the fans running OK? Did you ever remove the heatsinks from CPUs, and if you did, did you replace the thermal paste?
As an aside, if one removes the CPU heatsink, Intel recommends cleaning the CPUs and heatsinks of old thermal paste and applying new paste. The old paste hardens, and does not conduct heat well if the heatsink is replaced with the old paste. I did not think it would make a big difference, and sometimes just put the heatsink back on a CPU with the old paste, until I tested a system and found the CPU was running 1 deg. C below Tj max. That never happened before, so I cleaned the old paste off the CPU and heatsink, put some new good stuff on it, and then the CPU ran at least 12 deg. C below Tj max at 100% load. FYI.