Buick 2006 Rainier - Manual (Page 332)

When to Add Engine Oil
If the oil is below the L mark for the L6 engine or
the cross-hatched area at the tip of the dipstick for
the V8 engine, 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 5-105.
Notice: Do not add too much oil. If your engine
has so much oil that the oil level gets above
the cross-hatched area (F) that shows the proper
operating range for the L6 engine or above the
cross-hatched area for the V8 engine, your 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.
L6 Engine
V8 Engine
5-16