Buick 1994 Century Owner's Manual page 192

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.
I
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. Pon't spill coolant on .a hot
engine.
190