Buick 2009 Enclave Owner's Manual page 298

How to Add Coolant to the Cooling
System (3.8L V6 Engine)
Turn the pressure cap slowly counterclockwise until
it first stops. Do not press down while turning the
pressure cap. If you hear a hiss, wait for that to stop.
A hiss means there is still some pressure left.
5-28
1. You can remove the
radiator pressure cap
when the cooling
system, including the
radiator pressure cap
and upper radiator
hose, is no longer hot.
2. Then keep turning the pressure cap, but now push
down as you turn it. Remove the pressure cap.
See Engine Compartment Overview on page 5-12
Engine Compartment Overview for more information
on location.
3. Open the coolant air
bleed valve located
on the thermostat
housing, near the
upper radiator hose.