Cadillac 2002 Seville Owner's Manual page 267

1. Park the vehicle on a level surface. 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
-
one quarter turn and then stop.
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 slowly, and
remove it.
5-18
3. Then fill the coolant surge tank with the proper
mixture, to or above the fill mark at the forward
edge of the surge tank.