A thermostat sets the minimum operating temperature of a cooling system. Max temp is determined by the capacity of the radiator, load on the engine, and airflow across the radiator core. Either get the radiator cleaned thoroughly, add a fan shroud and/or a fan that moves mor air, or increase the heat load capacity of the radiator. Also check for the possibility of combustion gases leaking past a head gasket by using a "block check kit" that has a liquid that changes color in the presence of combustion gases in the radiator. NAPA stores sell a very good quality of block test fluid- - - -better than the stuff sold by O'Reilly's or Advance Auto Parts.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!