GMC 2010 T-Series Owner's Manual page 165

When to Add Engine Oil
Notice: Do not add too much oil. Keep the oil level
between the ADD (C) and FULL (B) marks on the
dipstick. Under normal engine operation, the engine
oil level can increase above the FULL (B) mark as a
result of DPF regeneration. A small increase in the
oil level is normal. If the engine has so much oil that
the oil level reaches the wider portion (A) on the
dipstick, the engine oil must be changed as soon as
possible or the engine could be damaged.
If the oil is below the ADD
mark (C) on the dipstick,
add at least one liter/quart
of the recommended oil.
This section explains what kind of oil to use. For engine
oil crankcase capacity, see Capacities and
Specifications on page 5 85.
Add enough oil to put the
level somewhere in the
proper operating range.
Push the dipstick all the
way back in when
through.
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