Anything over 100c will begin to physically burn components and likely cause smoke, even though 100c isn't enough to cause smoke on its own you have to bare in mind that we are talking 100c at a sensor location, typically near some larger more critical component. If the temp at the sensor is 100c, more often than not, there are circuits leading to it that can be up to 10 times hotter given how tiny they are and this is hot enough to melt components and circuits.  Generally if anything other than a CPU/GPU reads a genuine 100c+ temp your board will be burning somewhere and you will smell it. At least that is my experience with these issues.