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Discussion Starter #1
The owner's manual for my 2017 2500HD Duramax doesn't say anything about changing the front and/or rear differential oils, there is only a maintenance schedule for the transfer case. The dealership DEFINITELY has a schedule in mind because they charge $139 per differential to do it and that's good money for the work.

How often should I change my differential oil (I'm at 43K right now) and any idea why it wouldn't be listed in the manual's maintenance schedule? Where would the schedule be listed other than the dealership's pricing sheet?

FYI, a local dealership charged $115 to change the fuel filter on a 2018 2500HD w/ duramax/allison. This is one of the easiest fuel filters I have ever changed, takes about 5 minutes and I can get a Delco filter for about $21 from Amazon, dealer charged $55 for the filter. The markup is a little beyond reasonable to my thinking.
 

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If you are running on the original differential oil, I would change it at 50k. You will need just over 2 qts for the front and 3.5ish in the back.

We typically recommend AMSOIL Severe Gear 75W-90 Gear Lube for our customers. It is a full synthetic that provides excellent protection and longevity. It has a 100k drain interval. Best of all it comes in a squeezable bag for ease of use.

If I can answer any questions, please let me know.

Take care,
 

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Where would the schedule be listed other than the dealership's pricing sheet?
Many years ago, when it was listed, it was 30k for severe duty. Syn 75w-90
Towing was severe duty.

Which I had to laugh at at the time, since the whole core of the truck's design was as a towing platform. :rofl
 

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Discussion Starter #4
Thanks for the reply. I still find in interesting that the owners manual describes how to check front and rear differentials and the proper fluid levels (1/2 inch below the fill plug for Duramax) but does not say anything about changing it. The maintenance schedule lists an interval for the transfer case but ignores the differentials. I'm wondering if GM has so much faith in the prescribed Delco synthetic oil they use that they no longer feel it is necessary to change the diff oil.
 

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Well, I got that wrong too. The front diff fills to the bottom of the fill plug, the rear diff fills to 3/4 inch below the fill plug for 6.6 Duramax 2500HD. Makes me wonder how many mechanics can keep this straight.
 

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wondering if GM has so much faith in the prescribed Delco synthetic oil they use
Years ago, I was in for something else on a Saturday and the Dealer had an Express Lane for oil changes and such, so I had them service the rear diff while I was there.
In plain view from the waiting room, I watched their process.

Was it a 'special' GM fluid that came out of the Parts counter? Nope.
4 qts of Mobile-1 75w-90....with the 4th left partial, as the correct fill level is 3.5 qts.
 

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The owners manual for 2017 specifies SAE 75W-90 Synthetic Axle Lubricant GM part #88900401, everybody including me has a lot more faith in the synthetics. I'm thinking that this is what was loaded in the factory, I haven't changed mine yet and like your experience, I don't really trust the dealers that much. Maybe because it's synthetic and some of the synthetic manufacturers are claiming 100,000 miles or better for normal service, perhaps GM doesn't require the oil to be changed anymore. If true, the dealer isn't going to tell you that, so where do you go for the gospel?
 

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so where do you go for the gospel?
https://www.duramaxforum.com/index.php?page=active_topics ?
marx

On my last rear diff service, I was WAY overdue. What came out was nasty, burnt my nostrils with the odor. And a few minutes after getting some on my hands/skin, it lit up on fire like they were soaked in battery acid.

Made we think about pouring it into my recycle bucket (will it eat thru?)....but I already had some engine oil in it to dilute, so went with it. :howdy

I wouldn't be waiting 100k.
 

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I change mine every 50k miles with mobile 1 75/90. Front and rear. It is easy to do. Actually on my first change I did it at 25k miles and then every 50k after that
 
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