Once the temperature of the coolant in the engine has reached the limit of the thermostat the thermostat opens and allows the coolant to move to the radiator to be cooled. That coolant is then replaced with coolant that comes from the radiator. In theory the coolant entering the engine has given up its heat to the air flowing through the rows of cooling tubes. If for one reason or another the radiator isn't doing its job then that coolant may not be much cooler than what just left the engine. Many people put in a cooler thermostat in the mistaken notion that the car will run cooler. A car with cooling system problems will not be cured by putting in a cooler thermostat. The engine would run cooler with a 160 degree thermostat than it would with a 180 degree thermostat IF the coolant manages to get cooled enough during its turn in the radiator.

I'm not sure what temp thermostat is called for in the Bxxf(t) engines. I am guessing 190 degrees.

Randy