Depending on your temperature, 10-30w. If the temp regularly gets below zero (F), then switch to 5-30w during colder months.
Regular 30w is what was recommended. But you can use the new multi grades (10w30,20w30, etc.) if you want to. Some people use the new Synthetics also but i would only use them on a newer motor with an oil filter. Not cost effective when changing oil at a maximum 3000 miles.
Use whatever type of oil the user manual specifies.
I build VW engines for sandrails.......for NEW rebuilds, during break-in process, I use a non detergent 30W for the first 25 miles. I then recheck timing, valve adjustment, carb (s) and change oil using a 15W40 (not synthetic) 10W40 is also good. These are both great for 1600cc. However, if you operate in EXTREME heat (+90 degrees) with a lot of stop and go traffic you may choose to use a 20W50 (non synthetic).
WHAT TYPE OF MOTOR OIL SHOULD I USE FOR MY 2004 NISSAN TITAN
10w30
I use mobile 1 full sintetice oil
5w30
5w30
no
10w40
10w30
10w30