i suppose with the warm weater coming on, there will be a few of these questions. that first line above 80 is 100 degrees. the auxilliary fans will kick in above that at around 105 - 107. under normal conditions, the M104 engine normally does not get up to the 100 degree mark but stop and go driving will do that. after running at highway speeds even some mild stop and go will get it over the 100 mark.
in answer to your second question - the aux fans will turn on at low speed when the A/C is on. it switches to high speed when the temps reach 105 - 107.
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"