Do this test to get a idea if the sensor is accurate or not, after the computer has been at idle for 15 minutes or so very carefully touch the base of the heat sink
40c to 49c = comfortably warm
50c to 55c = warm near hot have to pull away after 2 or 3 seconds
55c to 65c = hot need to pull away after 1 second
65c and above = burnt fingers
Report what you find back
You could also use a themometer and touch its probe to the base of the hs.
That should give you an indicator of how hot if its at 70 or above you wont be able to touch the heat sink at all.