Oldsmobile 1995 88 Owner's Manual page 210

How to Add Coolant to the Coolant
Recovery Tank
If you haven't found a problem yet, but the coolant level
isn't at FULL COLD, add a 50150 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.)
NOTICE:
In cold weather, water can freeze and crack the
engine, radiator, heater core and other parts. Use
the recommended coolant.