About 100 is normal.. Some will try to make you feel its to hot...

The thermostat starts opening at about 92 to 95.. thats near 100... opens all the way at about 107.. about 110..

The fan clutch comes in at about 105 to 110.. You can check it by parking nose to a wall on a hot day with the windows down and running the engine at about 2500 or so RPM.. that way there is little air going thru.. in a garage helps as the heat stays near the engine.. At about 105 to 110 you should hear the roar of the fan as the clutch comes in.. You should hear the electic fan come on about 100 to 115 degrees.. you may want some one to hold the engine at speed and you stand up front where you can hear better... Open the hood and you loose the heat.. If you have a newer car with twin fans.. they should go on high about 115..

All in all.. 100 C is normal in warmer temps.. about 100 to 115 is where every thing should be doing its job..

If you are running under 90ish C in warm weather.. Replace the thermostat.. You are causing engine wear by running the engine to cool and using extra fuel..

Ken