Where is the thermostat on a 1990 Toyota truck 3.0?

Follow the upper radiator hose from the radiator to the engine. The thermostat will be located behind the thermostat housing at engine end of upper radiator hose. Drain some coolant into a clean container. Remove upper radiator hose from thermostat housing. Remove the 3 bolts that hold the thermostat housing to engine. Remove thermostat housing. Remove thermostat. Be sure to install the new thermostat facing in the same direction as the old one was.