Hi stirgy, first of all Welcome to WebmasterWorld!
8 years is a respectable age for an UPS system. The batteries probably need replacing by now. Are you running your laser printer from the UPS? This is generally not recommended because of the high peak currents.
When a CPU reaches a state of overheating, it may already become damaged before the system is shut down automatically. This damage may no be severe enough to prohibit the computer from working, but it can make the system less stable. The strange core temperature reading could also be a sign of problems in the circuitry of the CPU. The only way to be sure is to replace the CPU, but this is a relative expensive operation.