GMC 1996 Sonoma Owner's Manual page 205

3. Fill
the radiator with the proper
m i x . up to
the base
of
the filler
neck.
4. Then fill
the
coolant
recovery
tank to
the
ADD
mark.
5.
Put the
cap back on
the coolant recovery tank.
but
leave
the
radiator pressure
cap off.
5-19