Replacing the thermostat on your car should be part of the routine maintenance plan. The thermostat controls the water flow from the radiator of your car to the engine block and if it is not functioning properly, your car can overheat or run too cool. The thermostat on the Cadillac Deville sits inside a unique two-piece water neck at the front of the engine. The water neck bolts to the intake manifold and passes water or coolant to the engine block’s water passages. New thermostats are readily available at most auto parts stores and many department stores with larger automotive departments.
Remove the cover from the radiator and set it aside. Be sure the engine is cool or the pressure in the cooling system may cause hot coolant to spray out when opened.
Position a drain pan under the petcock of the radiator. Drain the coolant until it is below the level of the thermostat housing on the engine. Close the petcock by hand.
Locate the two bolts that secure the upper thermostat housing to the lower thermostat housing and remove them with a wrench. Carefully pull the upper thermostat housing off the lower thermostat housing.
Remove the thermostat and O-ring from the thermostat housing. Install a new thermostat into the housing followed by a new O-ring. Be sure the thermostat is oriented in the housing with the spring down or it will not function properly.
Install the upper thermostat housing over the thermostat and install the two retaining bolts. Tighten the bolts evenly with a socket and ratchet. Torque the mounting bolt to 20 foot-pounds with a torque wrench.
Fill the radiator with new coolant at a mix ratio of 50 percent water to 50 percent coolant until the radiator is full. Start the engine and allow it to run until the thermostat opens. Continue to add coolant to the radiator until it is full.
Replace the radiator cap and visually check the system for leaks. If the thermostat housing is leaking, tighten the bolts a little more. If that does not fix the leak you need to take it apart again and check the O-ring inside.
