1991 420SEL @ 135+K
Using 5K oil & filter change intervals, 8 quarts of Pennzoil LongLife 15W-40 (dino) puts the level square in the middle of the dipstick.
Have never needed to add more between changes as the level always remained well above the low mark.
p.s. 8 quarts between changes is WAY excessive, IMHO, but the oil should never go out of grade because of so much fresh oil being added. I would certainly go with a heavier weight oil than a 0W-30 in AZ.
'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435