1996 Mercury Grand Marquis Owner's Manual - Page 259

The reservoir for the windshield washer fluid RWARNING Do not put windshield washer fluid in the container for the engine coolant. Use specially formulated windshield washer fluid rather than plain water, because specially formulated washer fluids contain additives that dissolve road grime. For safety reasons, washer fluids containing an appropriate antifreeze such as methanol should be used in freezing weather (temperatures below 32˚F [0˚C]). State or local regulations on Volatile Organic Compounds (VOC's) may restrict use of the most common antifreeze, methanol. Washer fluids containing non-methanol antifreeze agents should be used only if they provide cold weather protection without damaging the vehicle's paint finish, wiper blades, and windshield washer system. 257