Buick RIVIERA 1993 Manual page 227

Add engine oil at the engine oil fill cap next to the oil
dipstick.
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:
Look for three things:
.
sc
"SG' must be on the oil container, either by itself or
combined with other quality designations, such as
"SG/CC," "SG/CD," "SF,SG,CC," etc. These letters
show American Petroleum Institute (API) levels of
quality.
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