GMC 1997 Safari Owner's Manual page 268

When to Add Oil
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.
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.
What Kind of Oil to Use
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.
If you change your own oil,
be sure you use oil that has
the Starburst symbol on the
front of the oil container.
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 have your oil changed for you, be sure the oil put
into your engine is American Petroleum Institute
certified for gasoline engines.
You should also use the proper viscosity oil for your
vehicle, as shown in the following chart: