2004 Cadillac DeVille Owner's Manual - Page 314

If no coolant is visible in the surge tank, add coolant as follows: {CAUTION: Steam and scalding liquids from a hot cooling system can blow out and burn you badly. They are under pressure, and if you turn the coolant 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 surge tank pressure cap, is hot. Wait for the cooling system and coolant surge tank pressure cap to cool if you ever have to turn the pressure cap. {CAUTION: Adding only plain water to your cooling system can be dangerous. Plain water, or some other liquid such as alcohol, can boil before the proper coolant mixture will. CAUTION: (Continued) 5-34