To remove and install the thermostat for 2.0L and 2.3L engines, first drain the cooling system below the coolant outlet housing, ensuring to use a sealable container to prevent pets from accessing ethylene glycol antifreeze. Disconnect the heater return hose at the thermostat housing, remove the retaining bolts, and slide the housing aside. Turn the thermostat counterclockwise to unlock it, then remove the gasket and clean both mating surfaces. Check the operation of a new thermostat by placing it in boiling water; if it does not open more than ¼ inch, do not install it. Coat a new gasket with water-resistant sealer, position it on the engine outlet, and install the thermostat with the bridge inside the elbow connection, turning it clockwise to lock it. Position the elbow connection onto the outlet, ensuring the thermostat flange rests on the gasket, and install the retaining bolts. Reconnect the heater hose, fill the radiator, and operate the engine to check the coolant level. For 2.2L and 2.3L diesel engines, drain the cooling system, remove the thermostat housing retaining bolts, lift the housing, and remove the thermostat, cleaning the gasket surfaces. Use a new gasket, tighten the housing bolts to 14-21 ft. lbs., refill the cooling system, start the engine, and check for leaks. For the 2.8L engine, drain the cooling system, remove the thermostat housing bolts, and lift out the thermostat, ensuring to clean all gasket surfaces and use a new gasket, tightening the housing bolts to 12-15 ft. lbs. Refill the cooling system, start the engine, and check for leaks. For 2.9L and 4.0L engines, drain the cooling system, disconnect the battery ground, remove the air cleaner duct assembly and upper radiator hose, and remove the thermostat housing bolts. Clean all mating surfaces without sharp tools, ensure the sealing ring is properly installed on the thermostat, position it in the housing with the air release valve up, coat the mating surfaces with adhesive sealer, place the new gasket on the housing, and torque the bolts to 7-10 ft. lbs.
