Just got a 1990 W150, 318 V8, 4 spd, 4wd. I want to know what oil goes in the engine, i looked it up and it looked like 5w-30, but i wanted to ask people who know more about this, also transfer case and transmission fluid? What am i looking at there, i had a ‘91 dakota transfer case blow up on me, so I’m doing things differently this time…thanks

 

10W30 for engine
ATF for the tcase (it is not that particular)
Is the 4spd auto or manual? The manual takes gear oil - 80W90.

 

I run 10W-30 in my magnum motors. I believe that's book spec oil. Theses 5w oils are a more 21st century thing. If you live in the arctic circle maybe 5w-30. I would imagine that trans was ATF+2 new. However we're superseded to ATF+4 now and its backwards compatible. You wont find +2 on a shelf anywhere I don't imagine. Transfer case typically also used ATF. Does your truck have hub lockouts? Transfer case destruction is very unrelated to the oil type. Yes there is some extreme scenarios oil could effect it but its simply bearings, a chain and helical gears. If there's oil in it, it should be fine. Low oil is hard on it, worn out chain and drive shaft failure are the main transfer case failure causes. Keeping your lockouts engaged unless you anticipate needs 4wd is a great practice. I know my grandpas 1990 W250 does not have lockouts, so you might not either. I'm not familiar enough with what was optional those years.

EDIT: Good catch on the auto vs manual, I wasn't thinking there. My suggestion would be for an automatic only