1995 Buick Century Owner's Manual - Page 187

2.2 L Engine 3100 Engine The 2.2L (VIN Code 4) has one bleed valve located at the thermostat housing. 3.1 L V6 (VTN Code M): There are two bleed valves. One is located on the thermostat housing. The other is located on the thermostat bypass tube. 5-21