Buick PARKAVENUE 1994 Manual page 214

How to Add Coolant to the Radiator
1
" I
1.
You
can remove the radiator pressure cap when the
cooling system, including the radiator pressure cap
and upper radiator hose, is no longer hot. Turn the
pressure cap slowly to the 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.
I
3. Fill the radiator
with the proper
mix, up to the base
of the filler neck.
212