- The thermostat has a number stamped on it. That is the temperature at which the valve opens.
- Submerge the thermostat in water and gradually heat the water.
- Check the valve opening temperature with a thermometer. If it is not within range, replace the thermostat.
- Also test the thermostat valve lift. It should be open 0.31 in. (8mm) or more at 203°F (95°C).
- It is also important to check that the valve is fully closed when the thermostat temperature is below 104°F (40°C).
- Replace the thermostat if it does not fall within the above specifications.
Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.
- Position a suitable drain pan under the radiator drain cock and drain the cooling system.
- On the 1MZ-FE engine, you may have to remove the air cleaner cap assembly. Be sure to label all wiring disconnected.
- Disconnect the water temperature switch harness from the water inlet housing (except 5S-FE engines).
- Remove the oil filter on 5S-FE engines that are equipped with an oil cooler.
- On the 1MZ-FE engines, remove the heater hose covering the housing.
- Loosen the hose clamp and disconnect the lower radiator hose from the water inlet housing.
- Remove the two nuts from the water inlet housing and remove the housing from the water pump studs.
- Remove the thermostat and rubber O-ring gasket from the water inlet housing.
- Make sure all the gasket surfaces are clean. Clean the inside of the inlet housing and the radiator hose connection with a rag.
- Install the new rubber O-ring gasket onto the thermostat.
- Align the jiggle valve with the upper side of the stud bolt.
- Position the water inlet housing with the thermostat over the studs on the water pump and install the two nuts. Tighten the two nuts to 78 inch lbs. (9 Nm) on 4 cyl. engines, 14 ft. lbs. (20 Nm) and 69 inch lbs. (8 Nm) on 1MZ-FE engines.
Don't forget to install a new O-ring onto the water inlet pipe. Apply soapy water to the O-ring prior to installation.
- Connect the lower radiator hose to the inlet housing and install the hose clamp. On the 1MZ-FE engine, tighten the bolt retaining the water inlet pipe to the cylinder head to 14 ft. lbs. (20 Nm).
- Attach the water temperature switch connector.
- On the 1MZ-FE engines, install the heater hose removed.
- Install the oil filter and check the oil level if removed.
- If removed, install the air cleaner cap assembly on the 1MZ-FE engines.
- Fill the cooling system with a good brand of ethylene glycol based coolant.
- Start the engine and inspect for leaks.