engine temperature and thermostat

[e320talk]

Hello Experts,
I have a 2002 e320 station wagon 4matic with 97k miles. My engine temperature has always been 79C and did not fluctuate. Recently, the temperature went up to 100C while driving but then came back down. So I changed the thermostat using the same OEM part. Now temperature stays at 87C. Looked at my old thermostat and the temperature setting on that is 87C. So, why was my engine temperature at 79C with my old thermostat which was set at 87C?
With the new thermostat, my engine runs at 87C which is the correct temperature according to the thermostat. But I wonder if it should be running at 79C like it was with the old thermostat?
Thanks.