Buick RIVIERA 1993 Manual page 226

Engine Oil
It's a good idea to check your engine oil every time you
get fuel. In order to get an accurate reading, the oil must
be warm and the vehicle must be on level ground.
The engine
oil
dipstick.is
directly behind the engine
fan..
Turn off the engine and
give the oil a few minutes
to drain back into the oil
pan. If you don't, the oil
dipstick might not show the
actual level.
To Check Engine Oil:
Pull
'
1
out the dipstick and clean it
with a paper towel or cloth,
I.ii'
"
then push it back in all the
..
,
way. Remove it again,
When to Add Oil: If the oil is at or below the ADD
mark, then you'll need to add some oil. But you must
use tlwright kind. This section explains what kind of oil
to use. For crankcase capacity, see "Capacities and
Specifications" in the Index.