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Questions regarding differential fluid
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=1&t=51806		 Page 1 of 1
Author:  rlanda [ Mon Apr 12, 2010 11:53 am ]
Post subject:  Questions regarding differential fluid
The time has come to change the differential fluid (front and rear) in my '06 KJ.

And the immediate question is which fluid to use (which oil grade, syn or mineral, brand)?

I began the research in the forum and found a lot of times the same question. So, there is a lot of
information about the subject and don't pretend to ask the same thing again.

I've read almost every post about what fluid to use in the differentials, not only here but in other forums, including jeepKJ, jeepforum and even a dodge forum.

After all that, one thing is clear, there is not an absolute truth about it. Is more about what worked
for someone or what somebody else think or feels.

I've read about reasons for choosing 75W90 over 80W90 or 75W140. Also read alot regarding which is better for differentials: synthetic or mineral. That's a long, long discussion and I'm sincerely leaning towards thinking that mineral is better, why? because 1st: The main reason Crysler recommends 75W90 (not for towing) to be used on many differentials is MPG, not performance and 2nd, for the front is still recommending 80W90 mineral and the only conclusion I cant get to about why is that 75W90 in front is
not optimal for some reason. (That of course is 100% my opinion and totally argueable).

I know it wouldn't be necesary to question what owner's manual says, but as many of you, what I wanna do is
use only one oil grade for both rear and front differentials.

I have concluded that is best for me to use Mopar 80W90 mineral based on the next statements:

Here in Mexico City, Mopar 75w90 syn is $90.00 MN (aprox. US$7.00) a quart, Mopar 80W90 mineral is $95.00 MN (aprox. US$7.30) a quart, and MOPAR 75W140 syn is $420.00 MN (aprox US$32.30) a quart.

I don't tow anything and don't plan to do in the near future, so because of this and price, 75W140 is discarded.

Winter here is not so severe, it's difficult to see temperatures below 0° Celsius, so it doesn't matter too much if I choose 80W over 75W.


But then, after I've made my mind, came across with a store that sells Mobilube HD 85W140 mineral and is priced $63.00 MN a quart (aprox. US$4.85).


Then, here are finally my questions. Mobil 85W140 is ringing a bell (it's the cheaper one), and knowing that a heavier oil will affect MPG:

If I use Mobil 85W140 front and rear will that be a complete overkill?

Will the MPG increase so much that in the long term I kill the saving in extra fuel (or even get worse)?

Will a 140 grade oil put too much stress in the differential during normal use (not heavy)?

What is your experience with Mobil brand (specifically talking about gear oils)? I know in general is one
of the best and more than cheap is the reason that Mopar is overpriced in my opinion.

I hope somebody finds useful how i came to a conclusion, the only question left is to decide between 80W90 and 85W140.

And, if I finally choose 85W140 based on what you tell here, I'll check the MPG very very close, in order to have concrete measure of how the oil grade affects fuel consumption.

As always, thank you very much in advance for what you might say about this subject.
Author:  stumpjumper_09 [ Mon Apr 12, 2010 12:00 pm ]
Post subject:  Re: Questions regarding differential fluid
I use Amsoil severe gear. Don't really care about the weight when using a quality product in my opinion
Author:  JJsTJ [ Mon Apr 12, 2010 1:32 pm ]
Post subject:  Re: Questions regarding differential fluid
sounds like 80w90 would work just fine for you. if you plan is to change it exactly according to schedule, going w/ syn probably wouldn't be worth any added expense. (though for me peace of mind is worth it)


fwiw, i run Amsoil 75w110 Full Syn Severe Gear in both diffs of all my Jeeps.
Author:  huntbuggy [ Tue Feb 15, 2011 7:38 pm ]
Post subject:  Re: Questions regarding differential fluid
Hey rlanda did you end up using 80W90 finally?

Am in the same boat here in Canada - it looks like the dealer's is $32 a quart for 75W140 and cheap gear lube in synthetics is really hard to come by.

Can get 5 gallons of 80W90 for $42 but diffs aren't a place I really want to scrimp and save too much...

Will keep reading mineral dino VS. synthetic threads and keep shopping I guess. We'll see what the local Amsoil dealer has to say about gallon sizes of Severe Gear 75W140 or the long life synthetic 75W90 for the rear.
Author:  tjkj2002 [ Tue Feb 15, 2011 8:10 pm ]
Post subject:  Re: Questions regarding differential fluid
huntbuggy wrote:
Hey rlanda did you end up using 80W90 finally?

Am in the same boat here in Canada - it looks like the dealer's is $32 a quart for 75W140 and cheap gear lube in synthetics is really hard to come by.

Can get 5 gallons of 80W90 for $42 but diffs aren't a place I really want to scrimp and save too much...

Will keep reading mineral dino VS. synthetic threads and keep shopping I guess. We'll see what the local Amsoil dealer has to say about gallon sizes of Severe Gear 75W140 or the long life synthetic 75W90 for the rear.

The cheapest 80w-90 dino gear oil is about the best for your diffs,85w140 dino for severe duty.The qualities that make synthetics great for a forced oil system like in a engine or trans is not good for your diffs.
Author:  LibertyCRD [ Wed Feb 16, 2011 12:56 pm ]
Post subject:  Re: Questions regarding differential fluid
All I know is...synthetic gear oil made my rear diff. pop and shake and act a fool. I honestly thought my rear end was going out. I switched to regular dino fluid @ $3 bucks per quart from Walmart...cheapest stuff I could possibly find... and my diff. is as smooth as butter now. Not a single problem since.

And yes...I used LS additive both times. So that proves to me that synthetic is NOT better for the KJ rear diff.
Author:  67Customs [ Wed Feb 16, 2011 5:23 pm ]
Post subject:  Re: Questions regarding differential fluid
rlanda wrote:
After all that, one thing is clear, there is not an absolute truth about it. Is more about what worked
for someone or what somebody else think or feels.

Even my User Manual and my Factory Service Manual say two different things.
Author:  huntbuggy [ Thu Feb 17, 2011 9:05 pm ]
Post subject:  ...blame Canada
After a very thorough search I'm going to go the 80W90 mineral dino route. The dealer actually recommended it when I picked up friction mod today.

Canadians who want an exhaustive gear oil search I won't cross post it :

http://www.jeepkj.com/forum/showthread. ... post531471

I have a coupon for next week I'll use to get $5 off my $44.99 gallon pail of dino and be done with it for awhile.

Will have to embrace the suck... I have the crappy squeeze siphoners and REALLY want that $10 pump that fits 5-gal pail screwtops (2 in?) from Harbor Freight...

...too bad for rlanda and I they don't ship to Canada or Mexico. :cry:
Author:  huntbuggy [ Sat Feb 26, 2011 12:02 pm ]
Post subject:  Re: Questions regarding differential fluid
80W90 pump issue solved. Got a slightly larger version that doesn't leak like the plastic cheapies. Harbor Freight or Northern Tool has these (or Princess Auto if you're in Canada). This one has a pickup tube and extensions for pails, drums or barrels so might be a bit more useful in the garage or barn...

Image




Several at Northern...
http://www.northerntool.com/shop/tools/ ... hand-pumps

If you swing by my place should make for a quick diff fillup :lol:
Author:  Billwill [ Sat Feb 26, 2011 2:17 pm ]
Post subject:  Re: Questions regarding differential fluid
Stupid question probably but is your rear diff a Limited Slip? My 2002 CRD Sport has the LSD at the rear.
If so, apparently you also need to add some special Jeep additive to the diff when changing oil :?
Author:  huntbuggy [ Sat Feb 26, 2011 4:43 pm ]
Post subject:  Re: Questions regarding differential fluid
Billwill wrote:
Stupid question probably but is your rear diff a Limited Slip? My 2002 CRD Sport has the LSD at the rear.
If so, apparently you also need to add some special Jeep additive to the diff when changing oil :?


Yep. TrashLoc needs friction modifier. One 4 oz bottle per change (Mopar 04318060AB). The little bottles fit nicely at the filler plug to just dump in slowly.
Author:  Billwill [ Sun Feb 27, 2011 3:50 am ]
Post subject:  Re: Questions regarding differential fluid
huntbuggy wrote:
Billwill wrote:
Stupid question probably but is your rear diff a Limited Slip? My 2002 CRD Sport has the LSD at the rear.
If so, apparently you also need to add some special Jeep additive to the diff when changing oil :?


Yep. TrashLoc needs friction modifier. One 4 oz bottle per change (Mopar 04318060AB). The little bottles fit nicely at the filler plug to just dump in slowly.



Yeah the reason I raised this question is that I hope the OP (rlanda) is aware of this fact and will be checking if he has LSD before draining/replacing diff fluids. :BANANA:
Author:  Xodius [ Sun Feb 27, 2011 3:08 pm ]
Post subject:  Re: Questions regarding differential fluid
How does one tell if they have a LSD?
Author:  huntbuggy [ Sun Feb 27, 2011 4:47 pm ]
Post subject:  Re: Questions regarding differential fluid
On your 02 check for a sticker on the right hand side of the rear axle - it'll say traclock if so.

If your sticker is gone like mine, check your build sheet or get one / ask from Jeep:

http://www.jeep.com/wccsapp/universal/J ... category=U
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