Thick gear oil required for my Jeep

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I found an online OM that said my Jeep could use a 90 weight gear oil in both axles, but after a bit more clarification on a few Jeep forums (and proof with a factory service manual), the front Dana 30 does indeed need a 75w-140 gear oil regardless of having LSD or not. Regardless of what is required, many folks online still run a 90 weight conventional gear lube in severe conditions.. issue free.

A rear non-LSD D35 can use a 90 weight oil, but a 140 weight is preferred for severe use, which seems backwards to me. A member suggested I use a 140 weight oil because of my slightly oversized tires (31's) which I guess is a good idea. Thoughts?

Anyways, a 140 weight in the front and a 90 weight in the rear for open diffs and normal use just seems backwards even though it still would have been slightly less resistance. I have no preference one way or the other, but I'll admit I was looking forward to A.) Cheaper gear oil. And B.) Possibly getting that 1/10th of a mile better fuel economy (or whatever it would have been.)
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I should add the 1999 Grand Cherokee open D30 is spec'd for a 90 weight, but they "updated" the spec to a 140 weight synthetic for years '00-'04 without any mechanical changes done to the axle.

*Anything with the vari-lok or trac-lok (Jeep's LSD) needs the 140 synthetic which is understandable.
 
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I went to the dealer last week and bought the limited slip additive for my grandfather's 96' Cherokee (has Dana 35 & trac-lock). I asked what weight of gear oil to use and he ran the VIN and said 80w90?
 
That's another thing I don't get.. The WJ has a different spec than the XJ.

I am not sure on the differences between a WJ axle and an XJ axle, but I imagine they are quite (if not exactly) similar.

*My dads MJ calls for a 90 weight too.
 
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how much oil is in the front and rear diff? likely the front holds a lot less and will experience higher temperatures when it's transferring power than the rear diff.

what does the transfer case require?
 
Good point. The front holds about 1.25 while the rear holds like 1.8 quarts.

The transfer case is the selec-trac (2WD, Part time, full time and 4Low) and takes ATF+4.

The AWD Jeeps need a special Mopar fluid. Not sure on the viscosity.
 
My D30 front gets 75w90 and my D44A in the rear gets 75w140.

The D44A rear gets 75w90 if your jeep doesn't have the optional trailer tow package. So basically, severe duty gets 140.

Right now I have 90 in the front and 140 in the rear.

The REAL oil spec that doesn't make sense to me on these jeeps is ATF+4 in the transfer case. I really don't agree with that. All of my transfer cases are going to get 10w30 synthetic. ATF+4 would be okay if you never engage 4WD save for a few random times. But otherwise ATF+4 in a NP231, 242, 249 etc. is a terrible idea IMO.

Most transfer case builders recommend 10w30 syn.
 
Originally Posted By: DemoFly
My D30 front gets 75w90 and my D44A in the rear gets 75w140.

The D44A rear gets 75w90 if your jeep doesn't have the optional trailer tow package. So basically, severe duty gets 140.

Right now I have 90 in the front and 140 in the rear.

The REAL oil spec that doesn't make sense to me on these jeeps is ATF+4 in the transfer case. I really don't agree with that. All of my transfer cases are going to get 10w30 synthetic. ATF+4 would be okay if you never engage 4WD save for a few random times. But otherwise ATF+4 in a NP231, 242, 249 etc. is a terrible idea IMO.

Most transfer case builders recommend 10w30 syn.
I'm pretty sure the NP231 calls for Dexron III
 
Originally Posted By: DemoFly
The REAL oil spec that doesn't make sense to me on these jeeps is ATF+4 in the transfer case. I really don't agree with that. All of my transfer cases are going to get 10w30 synthetic. ATF+4 would be okay if you never engage 4WD save for a few random times. But otherwise ATF+4 in a NP231, 242, 249 etc. is a terrible idea IMO.


ATF works just fine in the TC.
 
Originally Posted By: Nick1994
Originally Posted By: DemoFly
My D30 front gets 75w90 and my D44A in the rear gets 75w140.

The D44A rear gets 75w90 if your jeep doesn't have the optional trailer tow package. So basically, severe duty gets 140.

Right now I have 90 in the front and 140 in the rear.

The REAL oil spec that doesn't make sense to me on these jeeps is ATF+4 in the transfer case. I really don't agree with that. All of my transfer cases are going to get 10w30 synthetic. ATF+4 would be okay if you never engage 4WD save for a few random times. But otherwise ATF+4 in a NP231, 242, 249 etc. is a terrible idea IMO.

Most transfer case builders recommend 10w30 syn.
I'm pretty sure the NP231 calls for Dexron III

Dex III, F, ATF+3, ATF+4.
 
I'll stick to whats recommended for the transfer case. I am sure DexIII and ATF+4 can be used interchangeably in transfer cases, but I already need +4. No need for more fluids.

The 249 however is one that requires special fluid because of the viscous coupling.
 
Atf+4 can probably get a gl4 lettering, its an ok tc fluid.
note that mother says that if you use dex3 you should
change oil more frequently in the tc....
 
The 231 TCase doesn't care as long as it's a thin oil. I (and many other off roaders) are pretty hard on our 231s and they hold up just fine on cheap ATF.

I think a 20 or 30 grade motor oil would still be thin enough to properly lubricate. I'll stick with cheap ATF.

A gear driven transfer case will have different requirements.
 
Exactly. A gear driven TC in say a Toyota will need that thicker gear lube. Our Jeeps have chain driven TC's.
 
The only reason I could see for running heavier oil in a WJ than a XJ is they are significantly heavier than an XJ. High end WJs are 1000 pounds heavier than a XJ.

I ran 80/90 front and rear for a while. Now have 80w90 in the front and 85w140 in the rear. 140 is very thick, especially in the winter. But I don't have to worry about it getting too "thin" during highway runs!

Someone on here used 75w90 Supertech synthetic in an 18 wheeler that called for 140 and reported lower differential temperatures and a decent (we're talking like .1 or .2 - but that's a lot to a truck) increase in fuel economy.
 
Lots of guys run 5w-30 in chain driven transfer cases and are very happy with how they perform with it. DexIII is roughly a 10wt hydraulic fluid and the transfer case doesn't have any special requirments for EP, the oil is there to lube bearings and chains and to provide some cooling. I'm told that the 5w-30 is less prone to foaming.

As for the diffs, the WJ is quite a bit heavier than the XJ so it is basically running severe duty just hauling it's own weight around, IMHO the front diff has always been undersized for the cherokees and I've always run 75w-140 in my Jeep axles.
 
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