Trying to determine the type of fluid I should be putting into the transfer case. I've seen many say different things, some suggest 30 weight oil, some suggest 20 weight. I've read that Dexron III is what is called out by GM, would Dexron VI work?

Just trying to determine what should be going in to ensure a long lasting, healthy transfer case.

Thanks

Lots to read on a search...

Many here feel that 5w30 or similar is a great replacement to ATF. Until recently, GM recommended ATF...I think Dex3 or Dex6 won't really make a difference. The current fluid that GM says to use is the Auto-Trac fluid (even in the non-auto tcases), presumably to get rid of the ATF vaporization issues...that change just happened recently though.

Take it for what it's worth really, need to research and make the decision that you are comfortable with.

I use 3 qts of Mobile1 synthetic extended performance 5w30. -Mark

5w30 motor oil.

5W-30 Syn Motor oil is the BEST!

FWIW, from when the truck was new, I noticed some drivetrain noise (ok, you had to listen for it, a slight howl) after running down the freeway and then slowing/coasting on the off-ramp.

After 5w-30 Mobil 1 Synthetic, I don't hear it any more. (Of course, it could be my hearing is worse.) It's been over 17k miles. I'm convinced.

And I only put a little over 2qts. through the normal fill hole (jacked up one side slightly to get a couple extra ounces in it).

Awesome, thank you for the replies. Looks like I'll be getting some 5w-30 synthetic for it.

If you do a serarch, there's a tech notice from the manufacturer of the T-case recommending 3 qts 5W-30. Based on that, I also went with Mobil 1.

I have read all the posts about using 5w-30 synthetic motor oil and the recommendations from Mike L. and many others. I changed my transfer case oil in July 07 to Transynd. The oil that came out after 90K was original but looked ok (still red and lots - no vaporization) I pulled the transfer case out today to add the adapt-a-plate from Kennedy diesel for piece of mind on the pump rub issue. I drained the Transynd and it was like new - red and clean. This is after 40K of hard driving and towing the trailer in my avatar. I took the case apart and it was perfectly clean and there were no metal filings on the magnet. The retaining clip was like new and completely in tact. There were no signs of wear. I installed Kennedy's plate and put the transfer case back in. I WAS going to add 5w-30 syn motor oil but, after seeing for myself how well the Transynd did, I decided to stay with the Transynd and added 2 quarts.

"If you do a serarch, there's a tech notice from the manufacturer of the T-case recommending 3 qts 5W-30. Based on that, I also went with Mobil 1."

Not exatly true. Close, but not quite. The article (IIRC) was from Rockland(?) or something like that, and I recall that they were a repair/reman place or something to that effect. The manufacturer is/or was NewProcess, but I think they got bought recently(?). However, the warrantor (GM) does NOT recommend engine oil in the t-case; they spec tranny fluid, appropriate to specific years.

As the story goes, the repair/rework company was alarmed to find that often the fluid level was low when units came in for repair. They mentioned that they suspected it had evaporated quickly. I wasn't there; I cannot comment as to WHY the units were low on fluid, but I have a good hunch. Many people are diligent on tracking engine oil levels, but the T-case often gets neglected. It, too, needs occasional checks. If the level was low, it's not the fluids fault; it's the owner's fault. Damage that is subsequent to low fluid levels can't be fairly blamed on any lubricant.

The company that wrote the article suggested the use of 5w-30 engine oil, in the mistaken belief that it somehow lasts longer in service because it doesn't evaporate as quickly. Wrong. The viscosity of 5w-30 (depending upon temperature) is near that of DEX III/Mercon based products, so they recommended that instead. Here, a little bit of knowledge can be dangerous. They thought that they were smarter than the engineers who did all the research and trials.

I will fully admit that using a 5w-30 engine oil may not hurt the t-case at all. There are plenty of people here who use it and have no problems. But there are also plenty here that use the recommended fluids (tranny based) with no problems either.

There has not been any definitive study in the aftermarket that shows one better than the other. I have researched this at great length. And since the aftermarket is void of any true proof, then I'll stick with what the manufactuer and warrantor spec; that is tranny fluid (DEX III or VI depending upon year).

Keep your fluid level up, and you'll not have any issues.

Except for pump rub, and NO choice fluid will stop that from happening. Only a preventative fix before failure will stop that.

http://www.dieselplace.com/forum/showthread.php?t=148592&highlight=rockland+gear+transfer+case