#1
Drain the engine coolant so that it falls below the thermostat level by opening the drain plug at the bottom of the radiator and draining it into a catch pan.
#2
Follow the upper radiator hose to the thermostat housing, remove the clamp with a screwdriver then pull the hose away from the thermostat housing.
#3
Remove the thermostat housing with a socket, extension and ratchet.
#4
Clean the old gasket off the thermostat housing and the engine with a scraper, using a light back and forth motion.
#5
Insert the new thermostat with its spring going into the engine.
#6
Position the new thermostat gasket onto the motor then secure the thermostat cover on top.
#7
Tighten the thermostat housing bolts snugly with the socket and ratchet. Do not over-tighten them or you will strip the threads.
#8
Reattach the upper radiator hose onto the thermostat housing and tighten the clamp with the screwdriver. Pour coolant into the coolant reservoir.
#9
Start the engine and check for leaks.
Read more: How to Replace the Thermostat on a 2004 Chevy Impala | eHow.com http://www.ehow.com/how_7148937_replace-thermostat-2004-chevy-impala.html#ixzz17ATO13QN