Chevrolet 1997 Monte Carlo Owner's Manual page 198

3. After the engine cools, open the coolant air
bleed valve.
3 100 V6 (VIN Code M): There are two bleed valves.
One is located on the thermostat housing. The other is
located on the thermostat bypass tube.
3.4L DOHC V6 (VTN Code X): There are two bleed
valves. They are located on the thermostat housing and
heater outlet pipe.