Things You Will Need
Replacement thermostat, Replacement coolant, Socket wrench and sockets, Torque wrench, Adjustable pliers, Hose clamp pliers, A new thermostat gasket for the six-cylinder, 5.2L and 5.9L engines, Gasket scraper, Lacquer thinner or acetone, RTV sealant, On 4.7L V8 engines a new O-ring
Disconnect the negative battery cable from the battery.
Drain the cooling system. Save the coolant if it is in good condition to reuse. If the engine coolant is old or is in poor condition, replace it with the appropriate coolant mixture. Coolant can be purchased in a premixed or concentrated liquid.
The upper hose on the six-cylinder, 5.2L and 5.9L engines leads from the radiator to the thermostat housing. On the 4.8L V8 the lower hose leads to the housing.
After locating the thermostat housing, squeeze the tabs on the hose clamps and move them back several inches on the hose away from the housing. (If the clamps are the screw strap type, loosen the screw/bolt and slide back on the hose in the same manner.) Twist and remove the hose from the housing. If the hose is stuck, use a pair of adjustable pliers near the end and twist the hose to break the seal. If the hose has deteriorated, cut it off and replace it.
Remove the bolts and detach the thermostat housing. If the housing is stuck, tap it lightly with a rubber head hammer. Some coolant will leak from the housing.
If the thermostat housing is damaged or shows signs of corrosion or pitting, it will have to be replaced.
Note how the thermostat is installed. Usually the spring side of the thermostat is toward the engine. On the six-cylinder, 5.2L and 5.9L engines, put a rag in the engine opening and use the gasket scraper (a sharp putty knife will also work) to clean all of the old gasket material and sealant from the housing and cover. When the old material is removed, remove the rag and clean the areas with lacquer thinner or acetone. On the 4.8L V8 engine simply remove the O-ring.
On the six-cylinder, 5.2L and 5.9L engines, place the new thermostat in the machined groove on the engine making sure that the proper end faces out. (As noted above, the spring end is usually the end facing the engine.) Apply a thin layer of the RTV sealant to both sides of the gasket and position over the thermostat on the engine. On the 4.8L V8 engine, install a new O-ring on the thermostat aligning the rubber tab on the inside of the O-ring with the notch on the thermostat. Then align the rubber tab on the outside of the O-ring with the notch on the thermostat housing and place the thermostat into the housing.
Install the thermostat housing and bolts into the engine and tighten to 16 FT-lbs torque.
Attach the radiator hose to the housing and tighten the clamp securely.
Refill the coolant to the system and then start the engine and allow it to reach normal operating temperature. Inspect the system for leaks. If any are detected, allow the engine to cool and tighten the hose clamps, bolts or replace the gasket and sealant or the rubber O-ring as necessary. Hopefully no leaks are detected and you will have a cooler running engine and heat when it's cold outside.
Auto repair can seem like an impossible task for the average car owner. However, replacing a car thermostat is a relatively straight forward car repair that can be accomplished with minimal tools and experience.
Tips & Warnings
Special hose clamp pliers are available at most auto parts stores.
Always allow the engine to cool before removing the radiator cap, draining the coolant or replacing the thermostat. Steam and hot engine coolant may be under pressure and their sudden release could result is serious burns.