I'm trying to diagnose a groan noise the drive train has been making on my 4x4 '02 Blazer, so I went to check if all my oil levels are where they should be.
When I went to check the transfer case oil level, a bunch of black goo came pouring out of the fill hole.

I changed the transfer case oil last summer in 2020 with AC Delco Auto-Trak II fluid, and I don't remember pumping enough into the case where it would pour out next time I open the fill hole. I measured out what my repair manual says it's capacity is.
I guess the oil expands when it breaks down?

My real question is: why has my transfer case fluid broken down as quickly as it did?
When I did it's first change in 18 years and 150k miles, the oil was super black.
Checking it again 8 months and 15k miles later, the oil is super black again.

My Chilton repair manual for the 2nd gen S10 says that transfer case oil is changed every 50k miles, but this oil after 15k miles looks like it needs to be changed again.
The Auto-Trak II fluid the manual says to use is a light blue when it's brand new. So, is it suppose to turn black 3/8ths into it's lifespan?

 

It sounds like your transfer case input shaft seal may be leaking, allowing transmission fluid to get into your transfer case. Is the transmission low at all?

 

No, it's not low at all right now. I have added maybe a few ounces to top it off a while back, but I haven't noticed any external leaks. I know I have a bad main seal that's leaking engine oil, so I wouldn't be surprised if all the seals need replacement.

 

I think I found my answer. I had actually put the wrong fluid in the transfer case when I did it's first fluid change.
I didn't realize there is a difference between the 3 button 4WD (2HI, 4HI, 4LO) and the 4 button (4AUTO) transfer cases.
When I saw in my Chilton repair manual that it said it uses AutoTrak II fluid, I went to for that misreading the terms when it said the AutoTrak is for the "automatic" and Dexron III ATF is for the "electric".

I put about 15k miles on the transfer case with the wrong fluid. you don't think this caused permanent damage, did it?

 

I doubt you did any damage. Maybe if you had put regular ATF in the Auto Trak transfer case... I would change it, run it for a couple of days, then change it again to make sure all the old stuff is out.

 

Great idea. I was planning to change it again at the next oil change to make sure I'm draining all the mixed fluid.

 

i kinda have a similar thing. fluid is real real dark but i do have an Autotrak NV246, wonder what kinda fun im in for..