Your Cadillac's thermostat has water or coolant flowing through it constantly. Like all car parts, it is eventually going to break down and need replacement at some point in time. Replacing the thermostat on your Cadillac Deville is a relatively uncomplicated process and certainly one that the average backyard mechanic can pull off with little trouble.
Locate the thermostat housing. Your Deville's thermostat will not be immediately visible because it is actually contained inside a housing unit. This unit is located directly between the two valve covers on your Deville's engine and will have a large radiator hose running into it.
Place a small bucket in your engine compartment near the radiator hose.
Use your ratchet and socket set to remove the two mounting bolts securing the upper portion of the thermostat housing to the lower portion. Pull back on the hose and angle it into the bucket to catch any coolant that might leak out.
Make a note of how the thermostat is facing in the housing, then remove the thermostat from the lower thermostat housing and discard it.
Use a razor blade to remove the remnants of the old thermostat O-ring from the top and bottom portions of the thermostat housing, then clean the housing parts off with your scouring pad and paper towels.
Apply a layer of gasket sealant to the thermostat housing, then press the new O-ring firmly into the sealant so that it wont slip or slide away during the installation process.
Insert the new thermostat into the thermostat housing in the same orientation that you noted in Step 4, then replace the top portion of the housing over the thermostat.
Replace and tighten down the two mounting bolts.
Open your radiator cap and pour back in any coolant that may have leaked into the bucket during this process.
