I have a recently built Core i5 2500 on an asus z68 motherboard liquid cooled with a corsair h70. idle temps are 35C as measured with aida64 and realtemp. prime95 stress tests and virtually any PC game causes the reading to jump into the 90c range almot immediately. I was alarmed by this at first, but the PC passed all stress tests, and despite the temps claiming to be 90c +, neither the case, nor the motherboard mount or cooling block were more than warm to the touch. I am in the process of verifying the actual temperatures with a laser thermometer (at least reasonably so) but I am completely convinced that the sensor is reporting incorrectly. Has anyone else experienced this? is there a way to calibrate the sensors?
I would suggest installing the latest BIOS version for your motherboard, also keep in mind that you do not need to worry about the cores temperature, only about the CPU temperature.
In this case, the maximum recommended temperature for the i5 2500 is 72.6, so as long as the CPU does not reaches above this temperature, it will be OK.
If you still believe that there is an issue, try testing the processor on a 2nd motherboard, to see if it causes the same behavior.