2009 Cadillac STS-V Owner's Manual - Page 359

How to Add Coolant to the Intercooler System Fill Neck (4.4L V8 STS-V Engine Only) 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: 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. 1. Remove the Intercooler System pressure cap when the Intercooler System, including the upper intercooler hoses, are no longer hot. Turn the pressure cap slowly counterclockwise about one-quarter of a turn. If you hear a hiss, wait for that to stop. This allows any pressure still left to be vented. 2. Then keep turning the pressure cap slowly, and remove it. 5-33