I have just purchased an Intel E8400 to upgrade a machine that was previously running an E6600. The installation was annoying because of the trouble in mounting the CPU cooler, as there always is. (If only they could think of a better way to do this!) But the new CPU works fine, with one oddity. According to the on-chip sensors, there is a full 14 C difference between the two cores at idle! This is concerning, of course. I have already tried remounting the CPU cooler (argh!) and actually changed the orienation since it is one of those "tower" coolers with heat pipes in it. I thought maybe the location of the pipes was making it cool one core much better than the other. But after a 90 degree shift the large difference between the two cores remains. There was only a few degrees difference between the cores in the E6600.
After checking the cooler very carefully, it looks properly mounted and really looks like the two cores just have different temperatures. Is this a sign of potential problems? Could the contact inside the heat spreader have been botched at manufacture? I have run a high load on the machine to see what happens, and the peak temperature isn't too bad. 53-54 C for the warmer core at nearly 100 percent load while transcoding video. The difference between the cores shrinks to about 10 C when both are at full load. So it doesn't seem to be a critical failure of the heat spreader. But the difference is still disconcerting. Are the heat sensors inside CPUs really that variable?