Please choose the correct steps for the size of engine that you have:
4.5L & 4.9L Engines
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Drain the coolant to a level below the thermostat housing.
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It may be necessary to remove the upper air filter assembly on some models.
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Remove the 2 bolts securing the upper thermostat housing to the lower housing.
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Remove the upper thermostat housing.
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Remove the thermostat and O-ring from the lower housing.
Thermostat installation—4.5L and 4.9L engines
To install:
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Install the thermostat and a new O-ring to the lower housing.
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Install the upper thermostat housing to the lower housing. Tighten the thermostat housing bolts to 20 ft. lbs. (27 Nm).
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Refill the cooling system using a 50/50 mixture of water and ethylene glycol antifreeze.
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Start the engine and check for coolant leaks. Allow the engine to come to normal operating temperature. Recheck for coolant leaks.
4.6L Engines
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Drain the coolant to a level below the thermostat housing.
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On some vehicles, access is easier if the front-end beauty panel and the air cleaner are removed.
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Remove the 2 bolts securing the thermostat housing to the intake manifold.
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Remove the thermostat housing.
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Remove the thermostat and O-ring from the housing.
Thermostat installation—4.6L Engine
Loosen the upper radiator hose clamp at the thermostat housing
Remove the upper radiator hose clamp from the thermostat housing
Remove the thermostat housing retaining bolts and . . .
. . . remove the thermostat housing from the engine
Separate the thermostat from the housing
To install:
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Install the thermostat and new O-ring to the housing.
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Install the thermostat housing to the intake manifold. Tighten the thermostat housing bolts to 18 ft. lbs. (25 Nm).
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Refill the cooling system using a 50/50 mixture of water and ethylene glycol antifreeze.
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Install the air cleaner and beauty panel, if removed.
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Start the engine and check for coolant leaks. Allow the engine to come to normal operating temperature. Recheck for coolant leaks.