1998 Buick Century Owner's Manual - Page 271

Checking Engine Oil Pull out the dipstick and clean it with a paper towel or cloth, then push it back in all the way. Remove it again, keeping the tip down, and check the level. When to Add Engine Oil If the oil is at or below the ADD mark, then you'll need to add at least one quartof 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. your engine has If so much oil that the oil level gets above the cross-hatched area upper mark that shows the proper operating range, your engine could be damaged.