2006 Cadillac STS-V Owner's Manual - Page 350

How to Add Coolant to the Intercooler System Fill Neck (4.4L V8 STS-V Engine Only) If you have not found a problem yet, turn the engine off and allow it to cool down, then check to see if coolant is visible within the horizontal tube section of the fill neck. If coolant is not visible, add a 50/50 mixture of clean, drinkable water and DEX-COOL® coolant to the fill neck. Be sure the Intercooler System, including the Intercooler System pressure cap, is cool before doing so. See Engine Coolant on page 5-27 for more information. {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. Your vehicle's coolant warning system is set for the proper coolant mixture. With plain water or the wrong mixture, your engine could get too hot but you would not get the overheat warning. Your engine could catch fire and you or others could be burned. Use a 50/50 mixture of clean, drinkable water and DEX-COOL® coolant. Notice: In cold weather, water can freeze and crack the engine, radiator, heater core and other parts. Use the recommended coolant and the proper coolant mixture. {CAUTION: Turning the Intercooler System pressure cap when the engine and intercooler are hot can allow steam and scalding liquids to blow out and burn you badly. Never turn the Intercooler System pressure cap, even a little, when the engine and intercooler are hot. 5-38