GMC TopKick 2007 Owner's Manual page 270

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.
270
Add oil at the engine oil
fill cap in the engine
compartment. Install and
fully tighten the fill cap
when you are through.
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.