2003 Cadillac CTS Owner's Manual - Page 338

When to Add Engine Oil If the oil is at or below the lower mark, then you'll need to add at least one quart of oil. But you must use the right kind. This part explains what kind of oil to use. For engine oil crankcase capacity, see "Capacities and Specifications" in the Index. NOTICE: Don't add too much oil. If your engine has so much oil that the oil level gets above the upper mark that shows the proper operating range, your engine could be damaged. The engine oil fill cap is located in the center of the engine compartment. See "Engine Compartment Overview" in the Index for more information on location. Be sure to fill it enough to put the level somewhere in the proper operating range. Push the dipstick all the way back in when you're through. 6-12