Buick PARKAVENUE 1994 Manual page 212

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 COLD" 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.)
NOTICE:
In cold weather, water can freeze and crack the
engine, radiator, heater core and other parts. Use
the recommended coolant.
210