Chevrolet Malibu 2007 Malibu Owner's Manual page 377

Turn the pressure cap slowly counterclockwise
about two or two and one-half turns. If you
hear a hiss, wait for that to stop. This will allow
any pressure still left to be vented out the
discharge hose.
1. You can remove the
coolant surge tank
pressure cap when
the cooling system,
including the coolant
surge tank pressure
cap and upper
radiator hose, is no
longer hot.
2. Then keep turning the pressure cap slowly,
and remove it.
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