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Oil in NP-203 w/ part time kit...

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Mike87, Oct 10, 2000.

  1. Mike87

    Mike87 Registered Member

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    I know this subject has been beaten to within an inch of its life, but I am now confused. I took my '75 K5 in for a transmission (TH350) reseal. At the same time they are going to do the transfer case. I asked what they were going to use for fluid in the tc. He told me all they ever use is 90 weight. I said that the manual calls for motor oil.

    So I went home and checked the manual again. It says that for conventional 4WD use gear oil (90 wt or equiv) and for full time 4WD use motor oil. Well, did they use the NP-203 in conventional 4WD? If so, mine is now a conventional 4WD (was full time) and should I use gear oil? or is there something with the pump inside that makes is not compatible with the heavier oil?

    Bottom line....what is the correct oil to use in my transfer case?

    Thanks,
    Mike (#87)
     
  2. Boss

    Boss 1/2 ton status Author

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    Dude, with the NP203, make sure you put motor oil in it. Like 10W30 or something. Gear oil would mess things up. NP205 requires the Gear oil. No matter what, 203 requires motor oil, even if it has been converted to part-time. Make sure you have a 203 though, if you're not sure if you do or not.
    Boss
    http://www.boss.coloradok5.com

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  3. realsquash

    realsquash 1/2 ton status

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  4. Boss

    Boss 1/2 ton status Author

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    I don't know about the doubler and how its set up, but I do know for sure that the NP203 alone requires motor oil.
    Boss
    http://www.boss.coloradok5.com

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  5. Blazer1970

    Blazer1970 1/2 ton status

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    Yes, motor oil in the 203. In the doubler set-up, you would use gear oil. The high/low gear set in a 203 is basically the same stuff that is in a 205.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  6. MTPockets

    MTPockets 1/2 ton status

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    id really like to know why you should use motor oil instead of gear oil also. ive been running 90 wt. gear oil in my P/T 203 for three years now, and it operates just fine.

    MTPockets.
     
  7. 6.2Blazer

    6.2Blazer 1/2 ton status

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    The reason you should use motor oil in the 203 is basically because that is what the manufacturer says to use.......
    The 203 was designed to use motor oil instead of gear oil, which means the tolerances of the lubricated parts, and the lubricating "system" are designed to perform at the optimum level with the much, much thinner motor oil. While you may not notice any difference in operation or relatively short term wear, I would say over the long run that an 203 running on 90w will wear out quicker than one run with the specified motor oil.
     
  8. Boss

    Boss 1/2 ton status Author

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    Damn, You run Gear oil in your 203. Your 203 will be in a world of hurtin soon if you don't change out that fluid and dump some motor oil in there. Reasons is the gear oil is way too thick for the 203 and will not lubricate the links in the chain. Your chain will defiantely not last as long as its suppose to. If you don't believe me and are satisified with how its performing now, then keep the gear oil in there. You might be sorry in the long run though.
    Boss
    http://www.boss.coloradok5.com


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  9. Steve_87K5

    Steve_87K5 1/2 ton status

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    Book says 30 weight oil.
    Thirty weight.

    I use thirty weight Caterpillar gear oil. Get it at Caterpillar dealer. Works for me.

    SteveB
     
  10. ken

    ken 1/2 ton status

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    The factory manual says 10w-40 for the 203. As a side note, the NP205 in my '88 dually crewcab runs ATF!! That's what the manual calls for!!

    ken
     
  11. Boss

    Boss 1/2 ton status Author

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    Ken, Your NP205 from your 88' dually must be connected to an Auto Transmission, am I right? B/c if that's the case, you could put ATF in your 205.
    I have a TH350 and the NP205 in my K5. I run gear oil. Someone told me to give ATF (Dexron III) a try b/c you can run it in there, but when I did, it didn't run right, plus I had leak problems that I didn't have with the gear oil. (I know, its not the ATF fault that my case leaks, but ATF didn't help either), but anyhow, I switched back to Gear oil and the problems are all gone.
    Boss
    http://www.boss.coloradok5.com

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  12. Mike87

    Mike87 Registered Member

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    Thanks for all the input. I definately have an NP203. It is the cast iron heavy mother. If the tranny shop puts gear oil in it, I will drain it and put regular motor oil in.

    Just wanted to be sure I wasn't crazy or something.

    Mike (#87)
     
  13. blazer72

    blazer72 1/2 ton status

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    Having spent a lot of time reading on this and having found the info in many places it looks like at first the 203 used 80 w 90 and the moved to motor oil and finaly was shipped with ATF same thing with the 205. I run syntec 75w90 in my 203 redution box and mobil 1 atf gear oil in the 205 t-case. The seal that between the 4500 and the 203 is not all that good is why the 203 get the sysntec. But the seal between the 203 gear box and the 205 is really 2 dubel lip ones back to back.

    On stock setups it was moust often ATF in eather the case if it was behind a auto trany to make sure no 80w90 got in the auto trany, Gear oil or motor oil was used depinding on the year in the ones behind 4 speeds.

    I understand the jeep thing I drive a BLAZER!!

    Ken
     
  14. Wheels

    Wheels 1/2 ton status

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    I was doing some research on this earlier this year and remember this site after reading a posting about a 205 today. This should answer the question on what type of oil to use in a 203. I heard of some of the northerners running ATF during the winter months and in the south, gear lube for hot conditions. I run synthetic 10w 40 in my 203. Check this site out for what you should run and what you shouldn't use and why: http://www.off-road.com/chevy/mm-np203/
     
  15. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    2 reasons.
    1. The chain requires a thiner oil to lube especialy in cold climates
    2. There is a pump in the tail shaft that feeds oil to the rear bearing for both lubrication and cooling. It's basicly a plastic spiral gear like a speedo drive. Gear oil when cold tends to bust that pump and the end result is the rear bearing runs dry and over heats and burns up.

    There is a lip in the tail housing that catches oil slung of the chain. The diferential in the tail runs in it and the pump for the tail shaft gets it's oil supply from it. When you convert to part time you MUST put the case in LOC 10 miles every 200 miles to get the chain turning so as to refill this resivior or you will again trash the rear bearing.
    Motor oil in the 203. Same flavor you run in your engine is fine weather it be a 10w 30 or a 20w 50. The multigrades will not hurt the case infact they may be better for the same reason as they are in an engine. Multi grades were not common in the 70's when the 203 was produced is why the manuals state 30 weight. Yes in cold climates ATF would be something you could use since it is less effected by low temps but a 5w 30 might be a better choice.


    Diging it in the dirt with my K5's
    Grim-Reaper
    http://grimsk5s.coloradok5.com/
     
  16. Eric78K5

    Eric78K5 1/2 ton status

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    When I bought my 78K5, the np203 had both front and rear seals blown. I found this out when I went to service it for the very first time changing out all the fluids in the Blazer. I drove that thing for over 2500 miles before I got the chance to replace the seals. I talked to the guy who I bought it from, and he said he had NEVER serviced the np203. Well, I replaced the seals, put in the required 10w30, and the thing is still running and pulling strong! And people knock the np203 for being weaker than the np205!

    Eric78K5
    K5-Because Size Matters!
     

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