Chevrolet 2003 Impala Owner's Manual page 292

4. After the engine cools, open the coolant air bleed
valve or valves.
3400 V6 BLEED
VALVE #I
3400 V6 BLEED
VALVE
#2
3400 V6 engine: There are two bleed valves. One
is located on the thermostat housing. The other
is located on the thermostat bypass tube.
3800 Series II V6 Bleed Valve
3800 V6 engine: There is one bleed valve. It is
located on the thermostat housing.
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