Cadillac 1996 DeVille Owner's Manual page 245

NOTICE:
In cold weather, water can freeze and crack the
engine, radiator, heater core and other parts.
So
use the recommended coolant.
A
CAUTION:
You can be burned if you spill coolant on hot
engine parts. Coolant contains ethylene glycol
and it
will
burn if the engine parts are hot
enough. Don't spill coolant on a hot engine.
A
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 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.