1996 Cadillac DeVille Owner's Manual - Page 244

A CAUTION: Adding only plain waterto your cooling system can be dangerous. Plainwater, or some other liquid likealcohol, can boil before the proper coolant mix will. Your vehicle's coolant warning coolant mix. With system is set for the proper plain wateror thewrong mix, your engine could get too hot but you wouldn't get the overheat warning. Your engine could catch fire and or you others could be burned. Use a 50/50 mix of clean water andDEX-COOL antifreeze. TM 5-21