Pontiac 2003 Vibe - Manual (Page 227)

5-16
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.
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”
in the Index for more information about the proper
coolant mixture.