Cadillac 2001 Catera Owner's Manual page 236

2. Then keep turning the pressure cap slowly, and
1. You can remove the coolant surge tank pressure
remove it.
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) 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.
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