How do you change the thermostat on a 1990 Toyota truck?

To change the thermostat on a 1990 Toyota truck, first, ensure the engine is cool and disconnect the negative battery terminal. Drain the coolant from the radiator, then remove the upper radiator hose and the thermostat housing bolts. Take out the old thermostat, clean the mating surfaces, and install the new thermostat, ensuring it’s positioned correctly with the spring facing the engine. Finally, reassemble the housing, reconnect the hose, refill the coolant, and reconnect the battery.