Try covering part of the radiator with a piece of cardboard to restrict the airflow through the core. If the temperature rises then, it might be necessary to use a 195 degree thermostat. Is the radiator an original equipment item, or has a newer, more efficient one been installed? In general, the thermostat controls the minimum temperature the engine runs, and the cooling capacity of the radiator sets the upper limit. A "too big" radiator can cool things down to the point that the thermostat can't raise the temperature sufficiently. Have you tried checking the thermostat to see where it actually opens by putting it into a pan of hot water on a stovetop?
Jerry
