2017 Corvette / 14.4k / ACDelco 75w90 gear oil

[dparm]

This is the third rear differential fluid change the car has seen. Mileage worked out to a tad longer (14.4k vs 11k) but overall track time was similar (22 hours vs 24 hours). The car has a dedicated differential cooler. Blackstone highlighted that iron came down even further despite the longer run and everything else is steady. They attributed the aluminum to something "benign" like oxides. Confusing to see it continue to rise, but I don't consider it a wear metal for a differential. Open to ideas. I'm now using Red Line 75w90 GL-5 gear oil instead of the OEM GM fluid.

Code

OIL             ACDelco    ACDelco    ACDelco
MILES IN USE    14,465     11,057     2,958
MILES           28,480     14,015     2,958
SAMPLE TAKEN    3/24/20    10/20/18   7/3/17

ALUMINUM        174        111        40 
CHROMIUM        1          1          1   
IRON            123        138        107     
COPPER          5          4          3      
LEAD            1          1          1
TIN             0          0          0
MOLYBDENUM      1          1          1
NICKEL          4          3          2
MANGANESE       4          6          7
SILVER          0          0          0     
TITANIUM        0          0          0
POTASSIUM       1          2          5  
BORON           67         62         56   
SILICON         6          7          7
SODIUM          7          7          9
CALCIUM         14         16         11  
MAGNESIUM       8          4          4     
PHOSPHORUS      2291       2103       2299
ZINC            18         16         20
BARIUM          0          1          3
     
INSOLUBLES      0.3        0.3        0.2 
WATER           0          0          0   
FLASHPOINT �F  390        380        380
SUS VIS 210�F  69.4       71.1       73.7
cSt @ 212�F    12.80      13.23      13.93
TBN             3.1
TAN             6.4        9.2

 

[benjy]

redline lubes are as good as it gets + besides protecting more they last longer. only downside of excesive changes is $$$

 

[RhondaHonda]

Any idea how much is left behind in the diff cooler when you change it? I'm looking to change my 2017 Grand Sport soon if anything because I'm bored.

 

[dparm]

Originally Posted by RhondaHonda

Any idea how much is left behind in the diff cooler when you change it? I'm looking to change my 2017 Grand Sport soon if anything because I'm bored.

Not sure, but when my shop changed it out, I gave them the gallon jug and they said they used "most of it". I can't remember if this is the process for the diff, MT, or both, but it involves putting fluid in and then putting the car in gear and running it at low speed for like 10 minutes -- then topping it off.

 

[RhondaHonda]

Thanks. I'll read up on the procedure before attempting.

 

[Emperors6]

Thanks for posting this. I'll keep an eye on your UOAs to compare to mine since I also have a C7

 

[jtwrace]

Aluminum could be your cooler coming apart internally.

 

[Emperors6]

I also have aluminum in my diff oil changes for my C7. It's reassuring you're also getting it, since it might be normal wear.