GMC 1998 Safari Owner's Manual page 274

When to Add Engine Oil What Kind of Engine Oil to Use
If the oil is at or below the ADD line, then you'll need
to
add at least one quart of oil. But you must use the
right kind. This part explains what kind of oil to use. For
crankcase capacity, see "Capacities and Specifications"
in the Index.
Oils recommended for your vehicle can be identified by
looking for the "Starburst" symbol. This symbol
indicates that the oil has been certified by the American
Petroleum Institute (API). Do not use any oil which
does not carry this Starburst symbol.
I
NOTICE:
Don't add too much oil. If your engine has so
much oil that the oil level gets above the
cross-hatched area that shows the proper
operating range, your engine could be damaged.
Be sure to fill it enough to put the level somewhere in
the proper operating range. Push the dipstick all the way
back in when you're through.
If you change your own oil,
be sure you use oil' that has
the Starburst symbol on the
front of the oil container. If
you have your oil changed
for you, be sure the oil put
into your engine is
American Petroleum
Institute certified for
pasoline enpines.
You should also use the proper viscosity oil for your
vehicle, as shown in the following chart:
6-12