1998 Cadillac DeVille Owner's Manual - Page 269

How to Add Coolant to the Coolant Surge Tank If you haven't founda problem yet, but the coolant level (2.5 isn't at the proper level inches (6.4 cm) below the base of the fill neck), adda 50/50 mixture of clean water (preferably distilled) andDEX-COOL' coolant at the coolant surge tank, but be sure the cooling system, including the coolant surge tank pressure cap, is cool for before you do it. (See "Engine Coolant" in the Index more information.) Steam and scalding liquids from hot cooling a system canblow out and burn you badly. They are underpressure, and if you turn thecoolant surge tank pressure cap even a little they can come out at high speed. Never turn the cap when the cooling system, including the coolant surgetank pressure cap, hot. Wait is for thecooling system and coolant surge tank pressure cap to if you ever have to turn cool the pressurecap. -- -- Adding only plain water to your cooling system can be dangerous. Plain water, or some other liquid likealcohol, can boil before the proper coolant mixturewill. Your vehicle's coolant warning systemis set for the proper coolant mixture. With plain water thewrong mixture, or your engine could too hot but you wouldn't get CAUTION: (Continued) 5-20