GMC TopKick 2007 Owner's Manual page 266

When to Add Engine Oil
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 348.
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.
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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.
The engine oil fill cap is
located near the engine
oil dipstick in the
engine compartment, on
the driver's side of
the vehicle.