Buick 1994 Century Owner's Manual page 217

When to Add Oil
If the oil is at or below the ADD line, then you'll need
to add some oil. But you must use the right kind. This
section 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.
Just 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.
What Kind of Oil to Use
Beginning midyear 1993, oils of the proper quality for
your vehicle will be identified with this new "starburst"
symbol, The "starburst" symbol indicates that the oil has
been certified by the American Petroleum Institute
(API), and is preferred for use in your gasoline engine.
I
You should look for this on
the front of the oil
container, and use only oils
that display this new
symbol.
You should also use the proper viscosity oil for your
vehicle, as shown in the following chart:
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