90 to 100 deg C is normal.... I'm not sure why you are obsessing over this. If it was less than 80 when you are working it, then it would be more of a concern to me. What is the temperature on the stat? It should be stamped on it somewhere.
@ tcartwri, i should be running 72 C actually, not 100+. over 100 and im boiling past 212 F, i should be at a safe 160-180 F and the thermostat may not even have been the correct one, its a long stem, the one i ordered from farmproparts.com says its a shortstem... and if this was normal temp, i would not have excess coolant blasting out the overflow hose after it passes 100... .
I'm guessing you know you should be running a 50:50 antifreeze:water mix, even in the hottest weather, because the antifreeze provides better heat transfer than plain water.
BTW, there's a lot of good information in that site concerning cooling systems.Water has a higher specific heat than an ethylene glycol or propylene glycol coolant mix. Therefore, it provides the best heat transfer performance in a cooling system. If a cooling system is marginal, that is, it only overheats on the hottest of days, then running with water as a coolant in the summer and an ethylene glycol or propylene glycol coolant solution during the rest of the year will probably solve the problem. Commercial coolant solutions provide cooling, anti-freeze protection, corrosion inhibitors to protect the metals in the cooling system, and a lubricant for the water pump. When running water as a coolant for maximum heat transfer, a product that provides a corrosion inhibitor and water pump lubricant should be added to the water.