1998 Buick Riviera Owner's Manual - Page 253

C: cking Engine Oil Pull out the dipstick and clean it with a paper towel or cloth, then push back in all the way. Removeagain, it it keeping the tip down, and check the level. When to Add Engine Oil If the oilis at or below the ADD mark, then you'll need to add at least one quart oil. But you must use the of right kind. This part explains what kind oil to use. For of crankcase capacity, see "Capacities and Specifications" in the Index. I NOTICE: Don't add too much oil. your engine has If so much oil that the oil level gets above the cross-hatched area that shows the proper operating range, your engine could be damaged. Add engine oil at engine oilfill cap next to the the oil dipstick. Be sure tofill it enough to put the level somewhere in the proper operating range. Push the dipstick all the way backin when you're through. 6-12