Chevrolet 1994 Astro Passenger Owner's Manual page 200

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.
2. Then keep
turning the
I
pressure cap, but
now push down
as you turn it.
Remove the
pressure cap.
3. Fill the Radiator
with the proper
mix, up to the
base of the filler
neck.
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