2003 Lexus GS430 Diff., M1 75W-90, 24,232 miles

[btanchors]

As part of the 60,000 mile service on my 2003 Lexus GS-430 (which I actually performed a bit early), I had the Engine Oil, Transmission Fluid, Antifreeze, and Differential oil analyzed. This posting is on the results for the Differential. I think it looks pretty good, except I was a bit surprised by the TAN level, which the vendor performing the analysis (Analysts, Inc) flagged for monitoring (i.e., it's high, but not yet to the Abnormal level).

This analysis represents Gear Lube that was in service for 24,232 miles, and an interval of approximately 28 months. The Gear Lube was Mobil 1 synthetic 75W-90. The diff holds about 1.5 quarts. It is a standard differential (not a limited slip). This is the first time I have performed a UOA on the differential. Comments? I was surprised at the somewhat high TAN. Sample was taken on 10 November 2007.

Iron - 55
Chromium - 1
Nickel - < 1
Aluminum - < 1
Lead - 1
Copper - < 1
Tin - < 1
Silver - < .1
Titanium - < 1
Silicon - 17
Boron - 271
Sodium - 6
Potassium - < 10
Molybdenum - < 5
Phosphorus - 2034
Zinc - 36
Calcium - 37
Barium - < 10
Magnesium - 1
Antimony - < 30
Vanadium - < 1

Total miles on unit: 56,769
Miles on this sample: 24,232
Total Solids: 0.2
Water, %Vol: Vis, CS, 40 degrees C: 102.0
TAN: 3.53

 

[Tempest]

Seems to have held it's Vis pretty well. TAN does seem high. Lab error?

 

[unDummy]

Diff fluid capacity seems small for the vehicle weight and HP level.

Smart move keeping fluid changed at regular intervals. This is why I recommend 30k intervals or less always.

Wear looks normal. M1 additive package is a solid GL5. No reason to use anything else unless you want to collect comparative UOAs.

 

[btanchors]

Tempest -

I agree the TAN is a bit high, and the lab (Analysts, Inc) flagged the TAN as significant and worthy of monitoring.

From looking at UOAs of other differentials in this forum (The few that exist, anyway) - I agree, the metal levels look great.

But, assuming the TAN measurement is correct, I am a bit puzzled. Doesn't high TAN result from high heat for the oil? The vast majority of driving on this interval was short distance, and I drive this thing like a baby. As I recall, I took only two long highway trips - perhaps about 400 miles in August heat.

Also, as indicated, this oil only has 24,232 miles on it.

Is there anything else besides heat that would cause TAN to go high?

 

[The Critic]

TAN may be a bit high, but you need to do a VOA of the gear oil to see what the TAN level starts out at.

 

[MolaKule]

See comments on TAN:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1037993#Post1037993

 

[SubLGT]

Originally Posted By: Tempest
Seems to have held it's Vis pretty well. .........


Looks to me like it has sheared out of grade. According to the viscosity chart on this site, the minimum 40C vis for SAE90 is around 130.

 

[Tempest]

Originally Posted By: SubLGT
Originally Posted By: Tempest
Seems to have held it's Vis pretty well. .........


Looks to me like it has sheared out of grade. According to the viscosity chart on this site, the minimum 40C vis for SAE90 is around 130.

It starts out at 106 cSt.
http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil1_Synthetic_Gear_Lubricant_LS_75W-90.asp

 

[SubLGT]

After 10,000 miles in the rear diff of my Subaru, M1 75W90 was sheared down to a 100C viscosity of 13.4 (min vis for a SAE90 rating is 13.5).