Most cars these days seem specifically designed to hinder their owners from performing do-it-yourself maintenance on them, even when it comes to the most simple of tasks. This is not the case, fortunately, when it comes to replacing the thermostat of the 2006 Chevy Impala. While it certainly not contain the most comfortable engine compartment to work in--the muscle cars of the mid-1960s will likely forever hold that distinction--the '06 Impala nevertheless provides relatively easy access to the thermostat.
Open the hood of the Impala and locate the thermostat housing. Find the largest hose at the top of your radiator, then follow it until it connects onto a portion of the Impala's engine block. The piece that to which the hose connects is the removable thermostat housing.
Use a jack to raise the Impala off the ground, then settle it down onto jack stands. Make sure the car is in park and the emergency brake is on.
Place a large container under the Impala's radiator. Drain the radiator into the bucket by loosening the clamp on the lower coolant hose with a flat-blade screwdriver, then removing the hose entirely so that the coolant flows into the bucket. Once the coolant stops flowing, set the bucket aside.
Use the screwdriver to loosen the clamp on the coolant hose connecting to the thermostat housing, then remove the hose from the housing completely. This will give you access to the bolts securing the housing to the Impala's engine block.
Use a wrench or ratchet and sockets to remove the bolts securing the housing to the engine block, then set them aside somewhere where you will not lose them. Loosen and remove the thermostat housing to reveal the thermostat.
Make a careful note of how the thermostat is oriented toward the Impala's engine block. You must install the new thermostat in the exact same way as the old one is installed. Remove and discard the old thermostat.
Use a scraper tool or a razor blade to remove any remaining bits of thermostat gasket from the bottom of the thermostat housing and from the engine block. It is important to get all the remains off; otherwise the new gasket will not seal properly.
Apply a layer of gasket sealant to the bottom of the Impala's thermostat housing, then press the new gasket against the sealant so that it sticks and makes a good seal.
Install the new thermostat in the manner you noted in Step 6, then replace the thermostat housing and secure it down with the bolts. Reconnect the hoses you disconnected--making sure that the clamps are tightened down so no coolant leaks--and refill the Impala's radiator with the coolant you drained out earlier. Use your jack to lower the Impala back to the ground.