2018 Chevy HD rear differential fluid low from factory

[wwillson]

I drained and replaced the rear differential fluid in my 2018 Chevy Duramax today and found only 2.75 qts where there should have been 4.3 qts. This is so irritating that I've put 13,000 miles on the truck since new with 9,000 miles of that pulling an 8,000+ pound trailer with low differential fluid. The assumption was that both GM and the dealer could be trusted to correctly fill the fluids, but my assumption was wrong.

I don't know of this is excessive wear metal on the magnetic drain plug?

 

[BrianF]

Doesn't look excessive. Another reason to pull the fill plugs and check level early on.

 

[PPWarrior]

It is still under warranty. Might be worth a check at the dealer. Desu.

 

[Tomioka]

According to Amsoil's website for the 11.5" rear end it takes 3.15qts / 10.5" rear end 2.75qts.

A lot of these AAM rear ends don't fill to the bottom of the fill port and say fill to 1-2" from the bottom of fill port.

 

[02SE]

It looks like typical break-in wear. I've always drained diff's shortly after break-in, and refilled for long-tern change intervals. After the initial break-in, wear is minimal, but I still like to get the initial wear metals out.

I have an AAM 11.8 axle under my '17 RAM 3500. Pretty much all it does is tow a heavy 5th wheel toy hauler. It had similar amounts of metal on the plug, at the initial post break-in change.

 

[SZR48207]

I had about the same amount when I changed the fluid in my Tacoma's diff at 30K.

 

[JMJNet]

Somebody suggested to me to check the diff fluid at every oil change.

May just want to monitor it after you change it, check it at around 500 mi and 1000 mi.
Make sure there is no oil spewing out of the air ventilation hole and all the bolts are intact.

 

[clinebarger]

It calls for a little over 3 quarts....So it wasn't really that low. 11.5/11.8 AAM's are some stout/long running differentials so I wouldn't lose any sleep over this.

 

[clinebarger]

Originally Posted by JMJNet
Somebody suggested to me to check the diff fluid at every oil change.

May just want to monitor it after you change it, check it at around 500 mi and 1000 mi.
Make sure there is no oil spewing out of the air ventilation hole and all the bolts are intact.



That's a little excessive, Diff leaks are easy to spot & make a pretty good mess before it's get low enough to cause issues. I bet A LOT of trucks never get checked or serviced.

 

[FlyNavyP3]

My friends 2016 Tacoma with no transmission dip stick was also UNDERFILLED from the factory. Apparently it was common on the trucks with a towing package that got external aux coolers.

Dealership refused to check it without a performance complaint. Came back a week later with a "slide bump" on the 3-4 shift. Dealership checked fluid then and had to add 2.3 quarts to get it full.

That reminds me, I should check the fluid levels on my new 4Runner.

 

[wwillson]

Originally Posted by clinebarger
It calls for a little over 3 quarts....So it wasn't really that low. 11.5/11.8 AAM's are some stout/long running differentials so I wouldn't lose any sleep over this.


The capacity differs on some of the 11.5 AAM by model year. My 2018 took 4.3 quarts, which is what I expected.

 

[4wd]

I already did all driveline fluids on my 2017 and 2018 Chevy trucks … they were full of oil and rear magnets very similar.
The front differential on one had "grey" gear oil … Z71 xfer case magnet loaded …
Rear fluids were pretty good … nothing metallic like the front (that magnet loaded) … but a bit black from factory crud …

Why you do this:

 

[demarpaint]

The wear metal collected on the magnet looks normal.

 

[WyrTwister]

My concept is the ring gear runs in the gear oil / lube ? Wonder if the factory is running them a little lower to save a tiny bit on the fuel economy rating ? What does that do to the wheel bearings ?

 

[4wd]

That Banks video on here showed the gear oil "wave" running pretty high in the case …

 

[BlakeB]

The 11.5 calls for 6.3 pints (3 quarts & 4.8 oz) according to amsoil. I'm not sure why they can't just put the bottom of the fill plug where they want the fluid level to be? I'm sure there's some reason AAM/GM did it the way they did, but I don't have any idea what that reason is.

 

[clinebarger]

Originally Posted by wwillson
Originally Posted by clinebarger
It calls for a little over 3 quarts....So it wasn't really that low. 11.5/11.8 AAM's are some stout/long running differentials so I wouldn't lose any sleep over this.


The capacity differs on some of the 11.5 AAM by model year. My 2018 took 4.3 quarts, which is what I expected.


Do you mean that's how much you could cram in it? The correct COLD SERVICE level for your truck is 17-21mm BELOW the fill port!

They are filled by Volume during production, Not to reach a certain level. Once the Hubs fill with oil.....The level will no longer be within the SERVICE level range. Of coarse the oil in the Hubs won't drain out during service, Along with the oil that soaked into the housing along with what clings to the other components......I'm surprised you got the volume of oil out you did.

I've argued this with people for years, If you really want the optimal amount of oil in your diff......
*Fill the diff to the bottom of the fill plug cold.
*Run the truck HARD as you can with a load. If you can put you hand on the rear cover for ANY length of time....It's not hot enough!
*Pull the fill plug with the diff still HOT, Let the excess fluid drain out.

 

[clinebarger]

Originally Posted by BlakeB
The 11.5 calls for 6.3 pints (3 quarts & 4.8 oz) according to amsoil. I'm not sure why they can't just put the bottom of the fill plug where they want the fluid level to be? I'm sure there's some reason AAM/GM did it the way they did, but I don't have any idea what that reason is.


So you can check the level HOT without the oil coming out of the fill/check port.

 

[BrianF]

When I do the axles, my 11.5 AAM included, I overfill so that I pump in a bit more as some starts to flow out. I drive it around for a couple days and recheck on a level surface. If it flows out a bit, then its fine. If it does not, add some more. Never failed me yet.

I recall my 11.5 had similar break in metal.

 

[4wd]

Must have filled mine 0.04" above the port since a few drops came out !!!