1995 Buick Riviera Owner's Manual - Page 195

Bow to Add Coolant to the Coolant Recovery Tank If you haven't found a problem yet, but the coolant level isn't atFULL COLD, 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, beater core and other parts. Use the recommended co-olant. 5-14