1994 Buick Regal Owner's Manual - Page 192
1994 Buick Regal Manual
Page 192 highlights
How to Add Coolant tothe Coolant Recovery.Tank If you haven't found a problem yet, but the coolant level isn't at or above the "COLD" mark, add a 50/50 mixture of clean water (preferably distilled) and a proper antifreeze at the coolant recovery tank. (See "Engine Coolant'' inthe Index for more information about the proper coolant mix.) I NOTICE: In cold weather, water can freeze and crack the engine, radiator, heatercore and other parts. Use the recommended coolant. 190