Pontiac 1999 Sunfire Owner's Manual page 214

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. Turn the pressure cap slowly
counterclockwise (left) 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.
5-16
2. Then keep turning the
pressure cap slowly, and
remove it.
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