Chevrolet 1994 Astro Passenger Owner's Manual page 198

How to Add Coolant to the Coolant Recovery Tank
If you haven't found a problem yet, but the coolant level isn't at or above
the FULL mark, add a
50/50 mixture of clean water (preferably distilled)
and a proper antifreeze at the coolant recovery tank. (See "Engine Coolant"
in the Index for more information about the proper coolant mix.)
. .
. .
I
NOTICE:
In cold weather, water can freeze and crack the engine, radiator,
heater core and other parts. Use the recommended coolant.
When the coolant in the coolant recovery tank is at or above the FULL,
mark, start your vehicle.
If the overheat warning continues, there's one more thing you can try. You
can add
the
proper coolant mix directly to
the
radiator, but be sure the
cooling system
is
cool before you do
it.