Thermostat Cover Location on 4-Cylinder Models
The thermostat cover on 4-cylinder models is located behind the water pump.
Thermostat housing location on 6-cylinder models
Thermostat housing (indicated by the arrow) located behind the intake manifold above the gearbox.
General check
1. Measure the coolant level, check the drive belt tension and the operation of the temperature sensor.
2. If the engine takes too long to warm up, the thermostat is most likely stuck open. Replace the thermostat.
3. If the engine is overheating, check the temperature of the upper radiator hose, if the hose is not hot, then the thermostat is stuck in the closed position. Replace the thermostat.
Checking the Thermostat
1. To perform a more thorough inspection, the thermostat must be removed from the engine.
This material is taken from a resource ToyotaMan
2. If the thermostat does not close at room temperature, it is faulty and must be replaced.
3. Place the thermostat in a container of cold water (thermostat is closed).
4. Heat the water in the container and monitor its temperature. The thermostat should not touch the walls and bottom of the container.
5. Record the thermometer readings when the thermostat is just beginning to open and when it is fully open. Compare the values obtained with the technical requirements.
6. Replace the thermostat if it does not open or close or is stuck in any position.
Replacement
1. Disconnect the negative battery cable.
2. Drain the coolant from the radiator. Disconnect the radiator hose from the thermostat housing or from the inlet tube.
3. On 4-cylinder engines, disconnect the inlet pipe from the thermostat housing. Remove the oil filter for better access.
4. In 6-cylinder engines, remove the air valve cover and nuts (indicated by arrows) at the rear of the engine. Slide the wires to gain access to the thermostat cover bolts.
5. Disconnect the inlet pipe (indicated by the arrow) from the cylinder head and disconnect the tube from the thermostat housing (6-cylinder models).
6. Disconnect the fasteners and wires from the thermostat housing and remove the housing.
7. Remove the thermostat from the housing.
8. Clean the mating surfaces and install a new gasket.
9. Install the thermostat and thermostat housing in the reverse order of removal.