Rear Differnetial Fluid Revisited
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Joined: Nov 2004
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From: McKinney, TX
One thing that I know for sure about oil concerns in our diffs is that I would NEVER use the Mopar stuff. Our axles come with the Mopar fluid, no break-in additives, just their recommended oil. Since I always get an oil sample done when I change the crankcase oil, I thought 'What the heck, I'll send in a diff sample just to see what it says' - kind of the curiosity killed the cat mentality. So, when I change out my diff the first time and was switching to the Amsoil 75w140 I caught a samlpe and sent it in.
This was my written comment from the lab:
"Suggest inspecting this unit for EXCESSIVE WEAR, suggest flushing system, TITANIUM is at a SEVERE LEVEL; TITANIUM SOURCES may be alloy metal from ROLLING ELEMENT type BEARINGS, SHAFTS, or as a CONTAMINENT from COATINGS or PAINT; Visconsity is SIGNIFICANTLY LOW; Gear and/or bearing metal is at a MINOR LEVEL . . "
I sent in a sample of the original diff fluid the truck came with at 5K miles. More than likely the high titanium came from assembly lube, factory crap so to speak. It was the visconsity that I had more concern about, only 5K, a few medium weight tows less that 10K, probably closer to 8K. I did flush the system, eyeball inspection showed no wear on any gears. My real point here is that no wonder DC raised the spec via a service memo to 75w140 for all diff changes after break-in. The manual is now incorrect per their service memo. DC should have taken the time to notify us all via mail regarding this issue. I asked my dealership about diff fluid and they told me about the service memo raisisng it to 75w140, also read it over on the Carson Dodge site. There HAVE been diff failures on several trucks, maybe someone ran an oil analysis like I did and found out these diffs and the Mopar fluids are not very compatible. All I know is that if I have any problems with my diff I will be all over DC about the break-in fluid, and I DO have an independent analysis to prove their fluid was substandard at 5K.
I also had high numbers in Wear metals - Iron (633), Chromium (6), Aluminum (10), Titanium (165); Multi-source Elements - Magnesium (65), Lithium (19); and VISCONSITY - tested @ 100*c 14.0
Remember this is a diff fluid report not engine oil. Anyone going the recommended 15K before changing out their diff could be in some serious troubles. Maybe not at 15K, but later on after some miles this stock Mopar diff fluid could serve to shorten the lifespan of the diff in the overall.
CD
This was my written comment from the lab:
"Suggest inspecting this unit for EXCESSIVE WEAR, suggest flushing system, TITANIUM is at a SEVERE LEVEL; TITANIUM SOURCES may be alloy metal from ROLLING ELEMENT type BEARINGS, SHAFTS, or as a CONTAMINENT from COATINGS or PAINT; Visconsity is SIGNIFICANTLY LOW; Gear and/or bearing metal is at a MINOR LEVEL . . "
I sent in a sample of the original diff fluid the truck came with at 5K miles. More than likely the high titanium came from assembly lube, factory crap so to speak. It was the visconsity that I had more concern about, only 5K, a few medium weight tows less that 10K, probably closer to 8K. I did flush the system, eyeball inspection showed no wear on any gears. My real point here is that no wonder DC raised the spec via a service memo to 75w140 for all diff changes after break-in. The manual is now incorrect per their service memo. DC should have taken the time to notify us all via mail regarding this issue. I asked my dealership about diff fluid and they told me about the service memo raisisng it to 75w140, also read it over on the Carson Dodge site. There HAVE been diff failures on several trucks, maybe someone ran an oil analysis like I did and found out these diffs and the Mopar fluids are not very compatible. All I know is that if I have any problems with my diff I will be all over DC about the break-in fluid, and I DO have an independent analysis to prove their fluid was substandard at 5K.
I also had high numbers in Wear metals - Iron (633), Chromium (6), Aluminum (10), Titanium (165); Multi-source Elements - Magnesium (65), Lithium (19); and VISCONSITY - tested @ 100*c 14.0
Remember this is a diff fluid report not engine oil. Anyone going the recommended 15K before changing out their diff could be in some serious troubles. Maybe not at 15K, but later on after some miles this stock Mopar diff fluid could serve to shorten the lifespan of the diff in the overall.
CD
I read on here from, I think it was member 'Bluebull', who had stated that the original fill did have marker paint in the axles from AAM. Also, that the diffs get excessively hot during break in...Like 600 degrees hot. That that is why so many guys have rust on their stock diff cover because of the excessive heat peeling off the paint. But that after break-in, they cool dramatically and are fine.
I know when I changed out my original fluid at 15k it looked horrible. Runny, gray watery looking. Stunk. I was glad to get it out. Since then with the Mobil 1....like I said earlier...it looks brand new when it drains out.
I thought Mopar gear lubricant was just a repackaged brand of something else.
All of this is to say....I am not sure that the "Mopar" lubricant is necessarily bad,,,,,,,,,just that the original factory fill has a job to do and that is to break-in that diff and is designed that way. And, that the factory fill may not necessarily be the "Mopar" gear oil.
I just sent off an oil sample from my engine oil to Blackstone Labs. Now I wish I had sent of a diff sample too....to put my mind at ease about the Mobil 1 75w90 one way or the other.
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Joined: Aug 2006
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From: New Mexico
I was told directly by DC that our 2006 model trucks came with the same 75w90 Mopar diff fluid that is used by dealerships. I was also told by DC that a service memo DID exist regarding now using the 75w140 in the rear diff DUE TO AAM axle failures that seemed to be realted to the 75w90 being too low of a visconsity for the rear diff due to heat and towing.
While some can be 'comfortable' with one weight of oil or another, I am using what DC engineering and AAM recommend. I am still under warranty and if there is a problem I am using the suggested/recommended oil. These are decisions that everyone makes, I have made mine.
If you read transmission threads, one of the discussions had to do with temperature and lifespan of the tranny. For every so many degrees of temps your tranny life DOES decrease in mileage. The same applies to differentials and tranfer cases. The weight ratings of oil tell you the 'span' of protection. If it is clearly noted that our diffs during break-in can get as hot as 600*f, to me that also says they can get hot during use, whether empty or towing, the towing just puts more stress and work into the temp factor. So, I have chosen a diff fluid thats rated to spans the ranges better than the stock fluid, provides good lubrication, meets and exceeds the mfr recs. Also, I chose a company that will go to bat for me an their fluid in case I encounter any difficulties. I also bet that my future oil samples with what I have chosen will hold up in the visconsity levels over time, something that the Mopar fluid did not.
CD
While some can be 'comfortable' with one weight of oil or another, I am using what DC engineering and AAM recommend. I am still under warranty and if there is a problem I am using the suggested/recommended oil. These are decisions that everyone makes, I have made mine.
If you read transmission threads, one of the discussions had to do with temperature and lifespan of the tranny. For every so many degrees of temps your tranny life DOES decrease in mileage. The same applies to differentials and tranfer cases. The weight ratings of oil tell you the 'span' of protection. If it is clearly noted that our diffs during break-in can get as hot as 600*f, to me that also says they can get hot during use, whether empty or towing, the towing just puts more stress and work into the temp factor. So, I have chosen a diff fluid thats rated to spans the ranges better than the stock fluid, provides good lubrication, meets and exceeds the mfr recs. Also, I chose a company that will go to bat for me an their fluid in case I encounter any difficulties. I also bet that my future oil samples with what I have chosen will hold up in the visconsity levels over time, something that the Mopar fluid did not.
CD
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Joined: Nov 2004
Posts: 5,680
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From: McKinney, TX
CD....Thanks for the info. I will prob switch to the 140 weight next time.
Here a couple more threads about all of this for what they are worth...
https://www.dieseltruckresource.com/...d.php?t=139988
Post number 16 by Bluebull was what I referring too in my previous post.
https://www.dieseltruckresource.com/...d.php?t=142476
Here a couple more threads about all of this for what they are worth...
https://www.dieseltruckresource.com/...d.php?t=139988
Post number 16 by Bluebull was what I referring too in my previous post.
https://www.dieseltruckresource.com/...d.php?t=142476
Thread Starter
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Joined: Jan 2007
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From: Marshall, Texas
Well, its getting changed this weekend... I've already read too much in this thread to let it stay in another week. Kinda wish I had put that temperature tape on it the day I brought it home. But, I might have totally freaked out if it went past the 280 degree maximum range its designed for. (the temp. tape)
Thanks everybody, for all the insight,opinions and responses... thats what makes this forum so useful!
Funny thing about that dealership memo, I was just at the local dealership about 3 weeks ago and they told me to put 75/90 in it. I have about decided that for the most part, automotible dealership service departments are a good combination of don't know and don't care, which makes them pretty much useless.
As much as I hate to say this, the foreign cars are whipping the fire out of the US automakers in this area. My daughters new Honda Civic Si got a rock thrown up into the A/C condensor and knocked a hole in it. Dealership replaced it for free, and even gave her a loaner car. Even had a tech. come in last Saturday to get her car finished due to the fact that she had to get back to college that next monday.!!... Wish I could hear some stories like that from a US automaker service department....????
Thanks everybody, for all the insight,opinions and responses... thats what makes this forum so useful!
Funny thing about that dealership memo, I was just at the local dealership about 3 weeks ago and they told me to put 75/90 in it. I have about decided that for the most part, automotible dealership service departments are a good combination of don't know and don't care, which makes them pretty much useless.
As much as I hate to say this, the foreign cars are whipping the fire out of the US automakers in this area. My daughters new Honda Civic Si got a rock thrown up into the A/C condensor and knocked a hole in it. Dealership replaced it for free, and even gave her a loaner car. Even had a tech. come in last Saturday to get her car finished due to the fact that she had to get back to college that next monday.!!... Wish I could hear some stories like that from a US automaker service department....????
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Joined: Aug 2006
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From: New Mexico
One thing that my Father said to me when I started driving back in the 60's ALWAYS comes to mind - "Car Dealers, mechanics, repair garages, etc are in business to MAKE money . . Take their advice with a grain of salt, always do something the best you can with the best parts your hard earned money will get you, and learn how to fix it yourself." That advice has never failed me.
I am a small business owner, not automotive related, but I have a thriving business and Excellence in SERVICE and custoomer satisfaction is why my business thrives. I have traveled the world many times round, and every country but this one puts customer satisfaction and service at the top of the list. While using good, top quality parts can be more expensive up front, their overall use will get you your money back, and some change too. Same applies to oils, use good ones that exceed the manufacturers MINIMUMS, because that's exactally what the rec's are - the minimums.
CD
I am a small business owner, not automotive related, but I have a thriving business and Excellence in SERVICE and custoomer satisfaction is why my business thrives. I have traveled the world many times round, and every country but this one puts customer satisfaction and service at the top of the list. While using good, top quality parts can be more expensive up front, their overall use will get you your money back, and some change too. Same applies to oils, use good ones that exceed the manufacturers MINIMUMS, because that's exactally what the rec's are - the minimums.
CD
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From: Middletown In.
I know the service manual says 75-90 for our 11.50" rear axles but the first time I changed the oil I called a local dealership and was told by them that 75-140 full synthetic was what went in there. Also beware of quick lube places as most won't even remove your cover to change the oil but instead insert a vacuum tube to remove it. Who knows how much old lube is left and I always pull my axles out and drain my hubs as well but they won't. Read the fine print on your receipt! It's a release form that lets them go if your truck dies on you down the road. Been there done that with a place in Phoenix Az. lost the rear end out of my 2006 under a load because they put 75-90 normal gear oil back in. A week waiting on a axle housing to be shipped in and a putting my drive up in a motel. I was very lucky the dealer worked with me on getting it done under warranty. The axle housing is over 2k new for just the housing and chunk assembly. 
Someone said something about the axle reaching 600F and the paint peeling off the cover in the break end period. I find it hard to believe 600F. At this temp the oil will flash burn seals would as well. Getting hot enough you won't keep your hand on it yes they'll get that hot but 600F? I just can't see that without you replacing the whole rearend. I have heat treated steel when I ran machine shops and we normally annealed steel at 400F to release the stress and to bring some of the hardness out. To get ball or roller bearings to 600F will certainly be fatal to them under a load.
Mark
Someone said something about the axle reaching 600F and the paint peeling off the cover in the break end period. I find it hard to believe 600F. At this temp the oil will flash burn seals would as well. Getting hot enough you won't keep your hand on it yes they'll get that hot but 600F? I just can't see that without you replacing the whole rearend. I have heat treated steel when I ran machine shops and we normally annealed steel at 400F to release the stress and to bring some of the hardness out. To get ball or roller bearings to 600F will certainly be fatal to them under a load.
Mark
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From: Tacoma, WA
75W-140, this is a 140 weight oil that flows like a 75 weight oil in the winter.
The 140 weight oil would provide more protection under severe conditions, especially in warmer weather. The 140 should be a little thicker and pour more slowly.
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From: CALIFORINA
What about the additve you put in the diff .
When you changed your diff fuild over to synthic on a 2wheel drive did you add the bottle of treatment for the limited slip . It sound like the way to go is 90-140 is this right . 
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Joined: Aug 2005
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From: Ga.
75W-90, this is a 90 weight oil that flows like a 75 weight oil in the winter.
75W-140, this is a 140 weight oil that flows like a 75 weight oil in the winter.
The 140 weight oil would provide more protection under severe conditions, especially in warmer weather. The 140 should be a little thicker and pour more slowly.
75W-140, this is a 140 weight oil that flows like a 75 weight oil in the winter.
The 140 weight oil would provide more protection under severe conditions, especially in warmer weather. The 140 should be a little thicker and pour more slowly.
I put the 140 in the rear cause I figured with dual 34s (about to be 35s) and towin like I do sometimes it would be more beneficial. But now I am thinkin of just gettin a case of 140 and runnin it front and back.
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From: New Mexico
DODGEOG
If you use the severe gear you should not need to add the LS to the AAM LS axles. Having said that, you did not specify what year truck you have, so we also do not know what rear end you have. Take a minute and fill in your sig so we can better answer your questions AND WELCOME to the forum.
wap.
I'm running the 75w140 in both diffs, 35" tires, tow, hot climate, etc. I meet all the criteria for the heavier lube. Since all the synthetics seem thin to me, they all look like you're pouring water, I figured it would just be better to be using the heavier stuff. I have seen no change in fuel mileage.
CD
If you use the severe gear you should not need to add the LS to the AAM LS axles. Having said that, you did not specify what year truck you have, so we also do not know what rear end you have. Take a minute and fill in your sig so we can better answer your questions AND WELCOME to the forum.
wap.
I'm running the 75w140 in both diffs, 35" tires, tow, hot climate, etc. I meet all the criteria for the heavier lube. Since all the synthetics seem thin to me, they all look like you're pouring water, I figured it would just be better to be using the heavier stuff. I have seen no change in fuel mileage.
CD
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From: Ga.
Fuel milage is the least of my concerns when it comes to diff oil so thats not a problem for me.
I think I may try the amsoil or redline next time, just got to see what I can get a better deal on.
I think I may try the amsoil or redline next time, just got to see what I can get a better deal on.
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Joined: Jan 2004
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From: Delaware
"Mark
Personally I've been running the generic 75-140 full synthetic oil from Wal-Mart in both my trucks. The 05 has 195k on it and the 06 has 167k and both rear axles run just fine on the stuff."
This is what I will be running on my next diff oil change. 195k with heavy towing...I'm sold.
Personally I've been running the generic 75-140 full synthetic oil from Wal-Mart in both my trucks. The 05 has 195k on it and the 06 has 167k and both rear axles run just fine on the stuff."
This is what I will be running on my next diff oil change. 195k with heavy towing...I'm sold.
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From: Houston TX
I was looking into an oil additive and came across this thread. http://www.bobistheoilguy.com/images/lucas/lucas.htm
I think this guy sells Schaeffers, but it is interesting to see how the lighter weight fluid "climbs" at a lower speed, which could be a consideration for people who don't tow heavy, etc.
I think this guy sells Schaeffers, but it is interesting to see how the lighter weight fluid "climbs" at a lower speed, which could be a consideration for people who don't tow heavy, etc.
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From: OKC
I went in for some warranty work on my rear pinion today, and talked to the service manager about the Mopar lubes. He said that Mopar is built by Mobil. Like CD said, they are in the business to make money, but I also know that CD KNOWS what he is talking about. For what It's worth, I'm changing all my lubes over to Amsoil. Probably 75/110 in the diffs cause I only tow 5% of the time, the rest is empty highway miles. Just my .02