How do you replace thermostat on 1991 mr2 non turbo 2.2?

To replace the thermostat on a 1991 MR2 non-turbo 2.2, first, ensure the engine is cool and disconnect the negative battery terminal. Drain the coolant from the radiator and remove the upper radiator hose. Unbolt the thermostat housing to access the thermostat, remove the old thermostat, and clean the mating surfaces. Install the new thermostat with the spring side facing into the engine, reassemble the housing, replace the hose, refill the coolant, and reconnect the battery.