REMOVAL & INSTALLATION

See Figures 1 through 14

The thermostat is installed on the inlet side of the water pump. Its purpose is to prevent overheating of the coolant by controlling the flow into the engine from the radiator. During warm up, the thermostat remains closed so that the coolant within the engine heats quickly and aids the warming up process.

As the coolant temperature increases, the thermostat gradually opens, allowing a supply of lower temperature coolant (from the radiator) to enter the water pump and circulate through the engine.

A thermostat should never be removed as a countermeasure to an overheating problem. The vehicle cooling system should be serviced, necessary components replaced, correct coolant added and cooling system pressurized.

Fig. Fig. 1: Thermostat and gasket-4A-F engine

Fig. Fig. 2: Thermostat and gasket-4A-GE engine

Fig. Fig. 3: Thermostat and gasket-4A-FE and 7A-FE engines

Drain the cooling system and save the coolant for reuse.

CAUTION

When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

Fig. Fig. 4: Disconnect the sensor wiring from the thermostat housing

Fig. Fig. 5: Remove the hose from the housing

Fig. Fig. 6: Remove the bolts retaining the housing to the cylinder head ...

Remove the water inlet (disconnect electrical wiring) and remove the thermostat. Carefully observe the positioning of the thermostat within the housing. Clean all mounting surfaces before installation.

Fig. Fig. 7: ... then pull it from the cylinder head

Fig. Fig. 8: Pull the thermostat and gasket out of the housing

To install:

Fig. Fig. 9: Install a new gasket on the edge of the thermostat

On the 4A-FE engine, place the thermostat in the water inlet housing. Install a new gasket to the thermostat and align the jiggle valve of the thermostat as shown in the water inlet housing. The jiggle valve may be set within 10° of either side of the prescribed position (two types of thermostat are used).

Fig. Fig. 10: Jiggle valve positioning-1988-92 4A-FE engine

Fig. Fig. 11: Jiggle valve positioning-1988-92 4A-FE engine

Fig. Fig. 12: Place the thermostat into the housing with the jiggle valve set in between these points-1993-97 4A-FE and 7A-FE engines

On the 7A-FE engine, place the thermostat in the water inlet housing. Install a new gasket to the thermostat and align the jiggle valve of the thermostat with the upper side of the stud bolt. The jiggle valve may be set within 10° of either side of the prescribed position.

On the 4A-F and 4A-GE engines, place the thermostat in the water inlet housing. Install a new gasket to the thermostat and align the jiggle valve of the thermostat so that it is positioned above the water inlet housing.

Fig. Fig. 13: Align the jiggle valve to seat in this position-4A-F and 4A-GE engines

Install the water inlet (attach electrical wiring). Install the two hold-down bolts or nuts and tighten them to 7 ft. lbs. (9 Nm) (in steps). Do not overtighten these bolts!

Fig. Fig. 14: Tighten the two hold-down bolts or nuts in steps. Do not overtighten these bolts!

Refill the cooling system with coolant.

Start the engine. During the warm up period, observe the temperature gauge for normal behavior. Also during this period, check the water inlet housing area for any sign of leakage. Remember to check for leaks under both cold and hot conditions.

Engine & Engine Overhaul

REMOVAL & INSTALLATION