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Discussion Starter · #1 ·
The book calls for 15000 mile oil changes on the diffs in my o5 for severe service. Normal service interval doesn't say to change at all.


This seems to be one extreme to the other.

Does 75w90 synthetic gear oil really need to be changed at 15000 miles?

There are plenty of 30 year old trucks on the road that have never seen new gear oil>
 

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i just put 75w90 amsoil in my rear diff, the truck has 69k miles on it, and i dont know what was in it, but let me tell you it was BAD..... foamy and smelled really bad. i'm going to change mine every other oil change i think, so every 50k miles, which is also what amsoil recommends for severe use with the 75w90, 100k miles under normal conditions
 

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I did mine at 15,000 it was pretty funky looking, I put amsoil 75-140 back in for pulling the trailer, now have 45,000 on it, still looks good.
 

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Oil changes at 25K, rear diff changes at 60K with 80-140, use valvoline premium blue conventional oil and when compared with another truck I have in my fleet using amsoil and bypass filter, very little if any difference between them at 10, 20K and 40k miles. if you are towing, use the 80-140 in the rear differentials. Highly recommended.
 

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2012 3500 CCLB dually 4x4 auto Mini Maxx w/Anarchy Tunes studs 35's 5" exhaust S&B intake
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I filled both diffs with Amsoil 80w-90, and I don't plan on changing it for another 100k.
 

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I changed mine at 15K and it was ugly... I now have Amsoil SVG 75-90 back there, probably change it at 50K, then every 50K.. (I like to align things with big mileage marks)...
 

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Discussion Starter · #7 ·
Has dodge had some problems with their 11.5 rear ends? Why else would they call for 15000 mile drain intervals with synthetic gear oil?
 

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Just because its synthetic doesn't mean its extended life.. And 15K is only for severe service, and trust me after looking at mine at 15K you want to change yours.
 

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2012 3500 CCLB dually 4x4 auto Mini Maxx w/Anarchy Tunes studs 35's 5" exhaust S&B intake
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Amsoil states their AGL is good for 100K in cars, SUV, light & medium duty trucks. Severe service drain intervals at 50k.
 

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Discussion Starter · #10 ·
I've been using mobil 1 Stnthetic 75w90 which I assume is a good gear oil.

Does this oil still need to be changed at 15000?

some are claiming they are going longer on amsoil. Is it that much better than the mobil 1 ?
 

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id check the mobil1 at 15k, if you stick your finger in the plug and its foamy, change it, if not, got to 30k
 

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I would not run the factory gear oil much past past 5K. When I dropped mine it looked like gray 10 wt gear oil. If I was using Mobil One I would check it at 15K and if it looked good then I would check it every 5K there after as its not listed as a long life gear oil.

I'll add a bit more to ah64id post above. Even though a lot of oils are called synthetic does not mean there made from group 4 or 5 man made synthetic base stock. A lot of synthetic oils on the market today are just highly refined Group III crude based oil.
 

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Well, just from my experience, I haul heavy on a daily basis and if I had to change my fluid at 15,000 miles, I would suspect I would have lost a rear end by now, so changing at longer intervals must not be too bad, I will let you know at 400,000 miles, that is when I will change it next.

The most important thing is not to over fill it! about 1/4 inch below the fill hole is where you want it, and DCX recommends the 140 over the 90, due to the break down under heavy use, and if you are modded out, you are more than likely demanding a lot of work from the rear end.
 

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What does DCX stand for, I have never seen a 140 recommendation for the AAM.
 

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dodgerep knows his fluids for sure.
 

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IMO 15,000 is too often. GM uses the same axle and they don't spec a 15,000 mile change.
 

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IMO 15,000 is too often. GM uses the same axle and they don't spec a 15,000 mile change.
Then I would say you've never seen the OEM fluid after 15K....

GM also uses a smaller axle tube, so they obviously don't expect people to use there trucks as hard...
 

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The only trucks that Dodge said that should upgrade to 140 gear oil was the 1/2 tons trucks with smaller axles.
 

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The only trucks that Dodge said that should upgrade to 140 gear oil was the 1/2 tons trucks with smaller axles.
I could be wrong, but I would hate to use a 90 in my trucks. As a matter of fact, I would NEVER use it.

Well, as they don't put a 11.5 in a half ton, that information may not be correct. I will pull the TSB and see if I can post it.
 
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