Cadillac 2000 Seville Owner's Manual page 264

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 one
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.
5-16
3. Then fill the coolant surge tank with the proper
-
quarter turn
mixture, to or above the fill mark at the forward
edge of the surge tank.