Pontiac 2005 GTO - Manual (Page 200)

When to Add Engine Oil
If the oil is at or below the cross-hatched area at the
tip of the dipstick, then you will need to add at least
one quart 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 5-90.
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 in the cross-hatched
area. Push the dipstick all the way back in when you
are through.
5-14