I used 15W50 and 20W50 in my 300ZX most of its life. Those weights are actually spec’d in the owner’s manual as well as in the 1990-1996 Z32 fsm. I have an impeccable uoa with RP 20W50.
1996 Nissan 300ZX 5-speed,Arctic Pearl(#175 of 300)
Quaker State Ultimate Durability 10W30
2012 Honda Accord Coupe EX-L 2.4,auto,San Marino Red
Pennzoil Platinum High Mileage 10W30