Pontiac Vibe 2003 Owner's Manual page 256

How to Add Coolant to the Radiator
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.
Turn the pressure cap slowly counterclockwise until
it first stops. (Don't 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.
5-38
2. Then keep turning the pressure cap, but now push
down as you turn it. Remove the pressure cap.
3. Fill the radiator with the proper coolant mixture, up
to the base of the filler neck. See Engine Coolant
on page 5-29 for more information about the proper
coolant mixture.