Pontiac Vibe 2007 Owner's Manual page 302

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. 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.
2. Then keep turning the pressure cap, but now
push down as you turn it. Remove the
pressure cap.
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3. Fill the radiator with the proper coolant
mixture, up to the base of the filler neck.
See Engine Coolant on page 294 for more
information about the proper coolant mixture.