Cadillac 2006 STS - Manual (Page 331)

If the oil is below the cross-hatched area at the tip of
the dipstick, you will need to add at least one quart/liter
of oil. But you must use the right kind. This section
explains what kind of oil to use. For engine oil crankcase
capacity, see Capacities and Specifications on
page 5-116.
Notice: Do not add too much oil. If the engine has
so much oil that the oil level gets above the
cross-hatched area that shows the proper operating
range, the engine could be damaged.
See Engine Compartment Overview on page 5-12 for
the location of the engine oil fill cap.
Be sure to add enough oil to put the level somewhere in
the proper operating range. Push the dipstick all the
way back in when you are through.
V6 Engine V8 Engine
5-19