The 2002 Cadillac Deville comes equipped with two different types of engines. The 2002 Deville either has a 4.6-liter or a 4.9-liter engine. The thermostat replacement process is the same for both models. The thermostat allows the radiator coolant to flow into the engine block once the block has reached a certain temperature. Sometimes the thermostats will stick and will need to be replaced.
Park the 2002 Cadillac Deville on a level surface and open the hood. Wait for the engine to completely cool off before going any further.
Remove the cool radiator cap with your hands. Be sure to be wearing gloves.
Place the coolant catch pan underneath the front, driver's side of the radiator. Then, locate the butterfly plug on the lower driver-side of the radiator. The plug is a screw-in plastic plug with a small handle on its end. The coolant can be drained from the hole the plug stops up.
Turn the butterfly plug counterclockwise with the pliers. Once the coolant starts to run out, finish unscrewing the plug with your fingers. Wait for all of the coolant to drain into the catch pan and then screw the butterfly plug back into the bottom of the radiator. Tighten the plug with the pliers.
Go back to the top of the engine and locate the top radiator hose. One end of the top radiator hose attaches to the top of the radiator and the other end attaches to the thermostat housing. Unscrew the hose clamp from the top radiator hose and slide the hose back enough to get it off the thermostat-housing tube.
Slide the top radiator hose off the thermostat-housing tube. If the hose is hard to get off, use a flat-head screwdriver to pry it off. Stick the screwdriver in the end of the hose and keep prying until the hose loosens its grip, then slide it off.
Unbolt the two thermostat-housing bolts with the ratchet, extension and socket. Turn the bolts counterclockwise to loosen and remove them from the housing. Pull the thermostat housing off the top of the engine block.
Pull the old thermostat out of the inside of the engine block by pulling straight up on it.
Scrape whatever remains of the thermostat-housing gasket off the bottom of the thermostat housing and the top of the engine block. Make sure that the old gasket is completely removed from both areas, then wipe clean with a rag.
Slide the new thermostat into the top of the engine block with the spring facing downward into the block.
Apply a thin coat of the red high-temperature silicone to the bottom of the thermostat housing. Place the thermostat-housing gasket over the bead of silicone so that the two holes line up.
Slide the thermostat housing back over the top of the engine block and screw the two bolts in place. Tighten the two bolts down very tight with the ratchet, extension and socket.
Slide the top radiator hose back onto the thermostat-housing tube. Slide the hose clamp back in place over the hose and the thermostat-housing tube. Tighten the hose down tight with the screwdriver.
Fill the radiator back up with coolant. You can use new coolant or recycle the old coolant that you drained out. When the coolant level stabilizes at the top of the fill neck, crank the engine up.
When the coolant level starts to go down, keep adding coolant to the radiator until the coolant level completely stabilizes at the top of the fill neck. When the coolant level goes down with the engine running, this means that the new thermostat is functioning properly. Place the cap back on the radiator. Inspect for leaks around the thermostat housing and the top radiator hose. Turn the engine off.
