What fluid in NP203???
 

So what kind of fluid goes in this thing? I do have a part-time kit in it. Thanks.

The service manual calls for 30W. If your running a part time kit, make sure you put it in 4x4 at least 1 time every to weeks and drive a few hundred feet. This puts oil back in the rear output shaft bearing area.

my book says 10w40

10W40 in mine too.

thats what the books say i run 80 90 in mine have been for 3 years hasent gave me no problems the oil just dont seem thick enough to me

30wt,40wt,80w90,it all works,throw some Lucas oil stabilizer in,that will make any gearbox work smooth.

203s all use 10W40. I have an NP205 in my 88 crewcab dually, and it uses ATF!!! I thought about putting gear oil in there instead, but that's what the factory put in, and they have just a tad bit more engineering experience than me, so I left the ATF in it. :gmc:

10w40 in a 203