high memory temperature. high fan speed

as soon as i start the mac, the fan blasts full speed, and istat shows dim 2 temperature at 105+ Celsius, i am trying to find where is this sensor located to see what is wrong with it.

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

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crwdns2889612:0crwdne2889612:0 0

crwdns2942205:01crwdne2942205:0:

Have you changed anything, like the RAM or hard drive?

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crwdns2934285:0crwdne2934285:0