The only motor oil that I would use is Brad Penn 20W-50, its the old Kendal GT-1. Its green, thick, and sticks to everything!. Its tough to get off parts even with parts cleaner during a rebuild!. Now of course cost is another thing!. There are 4 quarts per gallon, so anyone complaining about paying $8.00 per gallon needs to price normal motor oil at over $2.00 a quart!.