NP203 fluid

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Big red square

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Is it ok to use 15w-40 diesel oil in np203 transfer case?
Also how much oil does it take roughly?
 

Snoots

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No, and HELL NO! 30W oil only. NOT 10-30W. Bone dry they take between 7 and 9 qts. Fill it until it runs out of the filler hole.
 

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I have a part time kit installed as well not sure if that makes a difference.
 

idahovette

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If it's part time, there should be a 90 degree elbow threaded into the case,with the plug into the elbow. Fill it til it runs out of the top then plug it. And when I worked at the Chevy dealership we filled it with whatever the engine had in it....30w, 10-30,10-40, or 15-40. All worked, mine has had 10-30 or 10-40 all it's life.......150,000 miles?....YMMV
 

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i thought they took autotrans fluid. my dodge did....
 

Turbo4whl

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This discussion for NP203 transfer case oil could go on for pages. GM recommended 10W40 in the early 1970's when these 203's first hit the scene.

Chrysler Corp. which had New Process Gear then, recommended transmission fluid. Since their engineers designed the gear box, did they know better?

About the engine oil, back in 1970 you had SE 10W40. Now we have SM or SN 10W40, what has changed? Lots of changes. Detergent engine oils are designed to suspend dirt partials (carbon) so the filter can pull them out. No filter and no need for it in the transfer case, so would non-detergent engine oil be better?

@Big red square Use 10W30 or 10W40 engine oil. Don't use heavy weight gear oil, will not lube the chain properly.
 

rich weyand

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The first number on oil is the viscosity when cold. As the transfer case never gets hot in an engine sense, the oil will never ride the temperature curve to the second number viscosity. The first number is the effective viscosity for the transfer case application. I would prefer running something like 20W50 for transfer case.

BTW: A trick with the NP203 with part-time kit installed.

The issue is that the rear output shaft bearing gets oiled by splash oil that runs down into some oilways in the case inside surfaces, then run down those oilways to the bearing. With the part-time kit, when in 2WD, there's no splash, so no oil delivery to the rear output shaft bearing. It doesn't need to be oiled constantly, but it needs to be kept wet or you will burn up the rear output shaft bearing, which is a major PITA to replace.

What I did was shift into 4WD every time I started the truck. The front Warn hubs were unlocked, so no issue. After about ten minutes, I would shift into 2WD. Since you are disengaging the splines, not engaging them, you can do that on the fly. This wetted the rear output shaft bearing every time I started the truck. On a long trip, I did the same thing whenever I had a rest stop or fuel stop.
 

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