2006 Cadillac DTS Owner's Manual - Page 324

Checking Coolant The engine coolant surge tank is located toward the rear of the engine compartment on the passenger's side of the vehicle. {CAUTION: Turning the surge tank pressure cap when the engine and radiator are hot can allow steam and scalding liquids to blow out and burn you badly. Never turn the surge tank pressure cap - even a little - when the engine and radiator are hot. The vehicle must be on a level surface. When your engine is cold, the coolant level should be at the FULL COLD mark, located on the side of the surge tank that faces the engine. For more information on location, see Engine Compartment Overview on page 5-12. 5-24