Thermostat Removal

Before concluding that the thermostat is the cause of a cooling system malfunction, check the coolant level, the drive belt tension of the auxiliary components, and the operation of the temperature sensor.

If the engine takes a long time to warm up (judging by heater output or the temperature gauge reading), this most likely means the thermostat is not closing. Replace the thermostat.

If the engine overheats, feel the upper radiator hose by hand. If the hose remains cold with the engine warm, this most likely means the thermostat is not opening and is preventing coolant from circulating through the radiator. Replace the thermostat.

WARNING: Do not drive the vehicle without a thermostat. Without a thermostat, engine warm-up will be slower. The electronic engine control system will then supply excess fuel as if the engine were warming up, which will increase fuel consumption.

Removal

On 4A-FE engines, the thermostat is located in the housing attached with bolts (Fig. 3.4.1.) to the upper part of the cylinder head on the transaxle side. On 3S-FE engines, it is located on the water pump at the front right of the cylinder block.

Fig. 3.4.1. Removing the thermostat cover, 4A-FE engine

· Drain the coolant.

· Disconnect the upper radiator hose from the neck on the thermostat cover.

· On 4A-FE engines, disconnect the cooling fan temperature sensor wiring from the thermostat cover.

· Remove the nuts and remove the thermostat cover from the studs on the housing.

· Note that the thermostat pin is located at the top, then remove the thermostat from the housing (4A-FE engines) or from the cover (3S-FE engines). Remove the rubber ring from the end of the thermostat.