2007.5 Dodge 6.7 Rear Differential Oil Analysis

[GBL]

This is my Blackstone analysis after 12,486 miles under pretty heavy towing. Recommended OCI under heavy loading is 15k miles. Under light loading they don't give an OCI. The truck has 84k miles. The oil has been changed at least twice previously. The first numbers are mine and the second are the universal averages (which is based on 17,740 miles). It's Mobil 1, 75W90 synthetic. The gear oil still looked new.

ALUMINUM 2 2
CHROMIUM 2 2
IRON 304 220
COPPER 6 2
LEAD 0 1
TIN 0 1
MOLYBDENUM 0 1
NICKEL 2 2
MANGANESE 14 15
SILVER 0 0
TITANIUM 14 13
POTASSIUM 1 2
BORON 130 210
SILICON 9 60
SODIUM 11 10
CALCIUM 24 58
MAGNESIUM 2 5
PHOSPHORUS 1704 1938
ZINC 66 34
BARIUM 1 1

Their comments were as follows:

GARY: Amended report to correct equipment type. Universal averages show expected metal readings after about 17,740 miles on the oil for a Dodge Ram. You haven't yet run this oil quite as long as average, though iron is already a little higher. Maybe your truck works harder than most and that explains the extra iron, which comes from steel parts. The viscosity was fine and no moisture was found. Insolubles are nice and low. No obvious problems were found here, though we'll be watching iron in the future. This oil should be fine with 3,000 more miles of use.

The previous oil had about 30k miles on it.

I'm thinking of using the 75W140. We run it primarily in warmer parts of the country.

Any comments?

 

[hounddog]

75w140 is not listed by AAM to use in these axels. Several years back I contacted AAM and asked. They said no to the 77w140. Said speced for 80w90 etc. I know folks with these axels towing 90% of time and only change diff.oil once every 100,000k. I know what the book says. Opinions please.

 

[lt1man]

I think you're over thinking it. 30k on rear end gear oil, is nothing. Way premature. Naturally there is going to be wear in it, I wouldn't worry about it. You can't run an analysis on every single fluid and worry when it comes back saying something like high iron.

I bet if you went 100k miles without changing it, no issue. I don't see why you wouldn't get 300k miles. Use what is recommended, don't over think it.

 

[dave1251]

75W90 Mobil One is a very good fluid. Follow you owners manual and continue to use high quality 75W90's like Mobil your differentials will last many many years and miles. I know some Diesel Rams that have 200K+ and the differential fluid is still on factory fill. Some people just do not change it out.

 

[CarbonSteel]

Wow...for only 13K miles on the oil that is a fair amount of iron is it not--especially with 84K miles on the axle (meaning that it is fully broken in and this was not the FF)? Although not the same axle, after 56K miles on the oil, mine only had 148PPM versus 304PPM for yours. Is this not the axle that had problems and thus the OEM recommendation for short OCIs when towing?

I could be confusing this with another axle, but I thought it was the one. I would not run this oil for 100K miles (and certainly not 200K or 300K) without checking it for a TAN to see how it is holding up--but that is just my opinion. I think you are doing the right thing--either by following the OEM recommendation or performing a UOA to keep tabs on the oil. Oil is cheap; axles are not.

 

[lt1man]

Let's not fear monger here. Even if he does change the oil, if the axle is wearing out the oil is not going to do anything! The gear oil is designed to go hundreds of thousands of miles. There is a magnetic drain plug to catch and shavings. So telling him to change the oil after 14k miles or when ever is not doing anything to solve the problem. The OP should just not worry about it.

 

[CarbonSteel]

Originally Posted By: lt1man
The gear oil is designed to go hundreds of thousands of miles.

So 200K or more without changing the axle fluid?

 

[dave1251]

I have seen it done and for some odd reason Ram owners are the biggest offenders of this practice. I do not believe any fluid should be used for 200K+ despite what synlube would tell us.

 

[CarbonSteel]

Originally Posted By: dave1251
I have seen it done and for some odd reason Ram owners are the biggest offenders of this practice. I do not believe any fluid should be used for 200K+ despite what synlube would tell us.

Is there a gear oil that will actually last 200K? I would guess the TAN would be very high as would be the wear metals. To each his or her own, but I would not do it--I love my truck more than that.

 

[dave1251]

I should have stated although I have seen it done, I do not recommend it. Also this practice is not exclusive to Ram owners, but it just happens to be from my records Ram owners do it the most often for pickup owners, I do not know why because changing gear oil is a very simple process and can be easier than changing motor oil. IMHO of course.

 

[CarbonSteel]

Originally Posted By: dave1251
I should have stated although I have seen it done, I do not recommend it.

 

[lt1man]

Gear oil comes from the factory in semi's rated for 500k. I'd rather change it after a few hundred thousand miles, or during a brake job when wheel seals are replaced.

 

[CarbonSteel]

Originally Posted By: lt1man
Gear oil comes from the factory in semi's rated for 500k. I'd rather change it after a few hundred thousand miles, or during a brake job when wheel seals are replaced.

Did I miss something? This is a OTR vehicle or a passenger truck?

 

[sw99]

Gee my old 92' F250 had almost 200K on the rear diff and the gears looked perfect when the cover was pulled...

 

[lt1man]

Again, people are just fear mongering about nothing. IF you wanna change it, 100k is reasonable. Anything other than that is just plain OCD. OTR or passenger truck makes no difference. It's a rear end, not an engine. It's synthetic, its practically the same gear oil. There is no difference between gear oil for a big rig and a truck, they both share the same weight and additives.

Stop freaking out. I'm sure it will be fine.

 

[GBL]

Wow. Thanks all for the responses.

In order:

This oil was specified by Dodge to be 75W90.

I thought the iron did look high to me.

I've had only one rear differentials go out on me and it was at ~150k...of course it was an F150. I had never changed it, the manual said it was ok for life. Experience makes me cautious on such promises.

The AAM 11.5" is used in both GM and Dodge.

There is no magnetic drain plug or drain plug at all on these. The cover is removed to drain the oil and it has a reusable gasket to do so.

My big concern was the iron content and what's considered abnormal or worse.

 

[CarbonSteel]

Originally Posted By: GBL
My big concern was the iron content and what's considered abnormal or worse.

Jim Allen has spent some time/research working with axles. I would PM him and ask for his thoughts.

 

[lt1man]

I'm sure Jim would say drive on.

 

[Jim Allen]

Under heavy towing, IMO, the iron your oil analysis is normal, if not a little better than normal. You did not get a full analysis, however. Ideally, you want to at least get TAN, if not oxidation (the latter is something Blackstone does not offer). IMO, the standard UOA methods are not particularly accurate one-shot measurements of and by themselves, because they only show the particles
I have not seen any info from AAM that lists a contamination condemnation level for their axles (either PPM or the more accurate ISO code) but the generic "worst case" ISO cleanliness condemnation level for gear oil is 22/20/17. The bottom edge condemnation level is around 19/17/14, so that's your range. Both these specs are for OPTICAL particle counts, not PORE BLOCKAGE contamination analysis Blackstone uses. Some interpretation is required if you want to compare optical and pore blockage.

Dodge/AAM recommends a 15K interval under heavy towing based on whatever the factory fill was and it no doubt has a generous safety factor built in. The iron is not outrageously high in your case but we really don't know the condition of the oil. You did not list the viscosity specs so we can't even see if it had sheared or not. Blackstone does do that, so please post the viscosity specs.

No Way would I recommend a 100K interval on an axle that works hard and only holds under 4 quarts. I do believe the interval can likely be stretch past 15K but it must be done with some knowledge and forethought. I wouldn't condemn the oil based on the iron alone. If the oil hasn't sheared much, it can at least go to 15K under the current conditions, perhaps longer. Without more info, my WAG is worth what you paid for it and the 15K interval is the safe bet. All the tests you'd need will likely cost more than the oil change. If it were mine, assuming the oil hasn't sheared, I wouldn't be afraid of 20K.

Here's a tip, though. Since you tow so much, install a diff oil temp gauge. AutoMeter makes a bung you can weld into a stamped steel cover. Aluminum covers can be tapped for a sender. Any oil temp gauge with a range from 100-300F can be used, but AutoMeter and others make diff temp gauges so marked. Monitor your oil temps. If you see temps running 250 or more long term, go with a shorter interval because the oxidation rate will be high. It's time-at-temp that counts, not the short spikes. Consistently high temps indicate a shorter interval. If around 200-220 under tow, no worries, and you can likely run a 30K interval no problem. Possibly more with a top quality oil.

If it's running very hot, consider a high capacity cover. In my tests, the Mag-Hytec (Google it) cover dropped an honest 15+ degrees off the temps and added a couple of quarts of capacity. It also has a magnet. Consider a magnet or magnetic drain plug got you diff. It will hold the big chunks and many of the smaller

 

[roadrunner1]

You are all correct, but I have seen a Dodge owners manual and they DO recommend 15,000 mi. intervals on certain rear-ends.

I don't know anyone who adhears to this ridiculously short interval, or why they have set it for such low miles.

Guessing that at some point in time there had to have been issues with this particular rear-end.

You can never go wrong following the owners manual.