http://www.pcplus.co.uk/tips/default.asp?pagetypeid=2&articleid=16113&subsectionid=383&subsubsectionid=91There can’t be an exact universal answer to that, but as a
rule of thumb we feel that 40 degrees Celsius is in the
right parish. We arrived at this figure by the following
unscientific method: AMD’s technical documentation states
that the difference in temperature between the die and the
bottom of the CPU is about 30 degrees. To this we add a
fudge factor to account for imperfections in the sensor,
which we guesstimate from information on several pages
including http://mikewarrior.freeservers.com.
So, if the maximum die temperature is 95 degrees, anything
over 55 begins to get worrying if you hope to be using the
same processor two or three years from now. Over 65 is
pushing into live fast, die young territory. The processor
won’t burn out unless things get really out of hand, but the
life expectancy reduces exponentially. At maximum core
temperature, it may be down to one or two thousand hours
according to the page at
http://www.digit-life.com/articles/pentium4athlonxpthermalmanagement.
Not all temperature monitoring is done externally. Intel
CPUs from the Pentium 3 onwards, and recent AMD CPUs, have
temperature sensors built into the processor die. Not every
motherboard actually connects to these, so they may be
unreadable without special equipment. However, if the sensor
can be monitored, then obviously you take the readings to be
close to the true core temperature.
Ian Sharpe