Chevrolet T-Series Owner's Manual page 188

When to Add Engine Oil
If the oil is below the lower hole 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 260.
Notice: Do not add too much oil. If the engine
has so much oil that the oil level gets above
the upper hole that shows the proper operating
range, the engine could be damaged.
188
What Kind of Engine Oil to Use
Look for these two things:
•
CJ-4 or CI-4
Oils designated as API CJ-4 or CI-4 are
recommended for your vehicle. The CJ-4 or
CI-4 designations may appear either
alone, together, or in combination with other
API designations, such as API CJ-4/SM.
These letters show American Petroleum
Institute (API) levels of quality.
Notice: Use only engine oils that have one of
these designations, CJ-4 or CI-4, for the diesel
engine. Failure to use the recommended oils
can result in engine damage not covered by
your warranty.
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.