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#219667 - 06/09/03 05:22 AM Mobil 1 Synthetic 75w90 gear oil
1maniac Offline

Registered: 10/11/02
Posts: 571
Loc: Pittsburgh PA
This is from the differential in my 1994 BMW 540i. Approx 2 quart capacity or so.

Time on oil: 14 months
Miles on oil: 6,862

Iron: 252
Chromium: 3
Lead: 0
Copper: 1
Tin: 0
Aluminum: 1
Nickel: 0
Silver: 0
Silicon: 1
Boron: 226
Sodium: 5
Magnesium: 0
Calcium: 12
Barium: 0
Phosphorus: 1577
Zinc: 7
Moly: 0
Titanium: 0
Vanadium: 0
Potassium: 0

Fuel: NA
VIS @ 40c cSt: 107.4
Water: 0
Soot: TR
Glycol: NA

TAN: 3.35
Oxid: 5.0
Nitr: 2.0

Results say no corrective action required.

I changed out the Mobil-1 with Amsoil 75w90 Synthetic ube.

#219668 - 06/09/03 05:49 AM Re: Mobil 1 Synthetic 75w90 gear oil
nicrfe1370 Offline

Registered: 02/25/03
Posts: 471
Loc: the state that looks like an u...
There are so few non-engine analyses here that it's difficult to interpret your results. Considering the mileage on the oil the iron does seem particularly high. With 25000 miles on Amsoil S2K 75W-90 in the rear diff of my Subaru WRX I had 167 ppm of iron.
Other than the iron it looks perfect. [Big Grin]

#219669 - 06/09/03 06:27 AM Re: Mobil 1 Synthetic 75w90 gear oil
Quattro Pete Offline

Registered: 10/30/02
Posts: 29949
Loc: Great Lakes
Being used to single digit iron numbers in engine oil analysis results, your iron figure definitely stands out, especially for such a short running interval. What is the recommended change interval for this car and which oil spec does it require (GL-4 or GL-5)? Which lab did the analysis? Did they provide you with universal averages that you can compare your results to?

#219670 - 06/09/03 06:37 AM Re: Mobil 1 Synthetic 75w90 gear oil
Al Online   content

Registered: 06/08/02
Posts: 15209
Loc: Elizabethtown, Pa
I think the problem here may be contamination. Unless the gearbox was totally and completely cleaned before adding new oil the amount of iron filings from initial wear-in is probably through the roof. This is just a wild stab in the dark though. [I dont know]

#219671 - 06/09/03 02:01 PM Re: Mobil 1 Synthetic 75w90 gear oil
Doug Hillary Online   content

Registered: 05/30/03
Posts: 5052
Loc: Airlie Beach Australia
reading OA results from diffs and gearboxes is a much different exercise from engines. Iron levels for one are always substantially higher

While I have not got any data from cars I have some data from EatonFuller on their components and samples analysis from ExxonMobil on my heavy vehicles which I will make available next week - for interest sake only

I change diff and gearbox oils on my cars and trucks within 3000 miles from new. This is a very important change as it removes production and "assembly" contaminants and allows no build up on seals. Then, they run on synthetics without change for 600000 miles or until sale

I have done this for the last 10 years with only occasional sampling to confirm the oil's status
We have far fewer seal failures than similar vehicles on mineral oils and 60000 mile oil changes


#219672 - 06/09/03 06:00 PM Re: Mobil 1 Synthetic 75w90 gear oil
metroplex Offline

Registered: 09/12/02
Posts: 1904
Loc: SE MI
I too break-in new factory rear ends and quickly switch to synthetics. I do this usually at 500 miles.

#219673 - 06/09/03 08:06 PM Re: Mobil 1 Synthetic 75w90 gear oil
metroplex Offline

Registered: 09/12/02
Posts: 1904
Loc: SE MI
usually oyu can find large chunks of metal on the magnet during break in. I found some crazy stuff with my Torsen, while I found just regular large chunks with a clutch posi (Dana 60 T-Lok)

#219674 - 06/10/03 09:44 AM Re: Mobil 1 Synthetic 75w90 gear oil
Jimbo Offline

Registered: 02/13/03
Posts: 1351
Loc: California, USA
BMW specs a GL-5 mineral lube change every "Inspection II" which is dictated by the dashboard service lights. I think this would normally be every 30,000 miles or so.

I switched my BMW over to M1 75W-90 last time with the intention of it being a "lifetime" fluid.

#219675 - 06/11/03 12:08 AM Re: Mobil 1 Synthetic 75w90 gear oil
1maniac Offline

Registered: 10/11/02
Posts: 571
Loc: Pittsburgh PA
I have no idea how often the original gear oil had been changed with the previous owner. I suspect it had been a LONG time [Frown] so I called the BMW dealer and asked them what kind of gear oil to use because the service manual states "with limited slip.....BMW SAF-XLS Synthetic Oil." The dealer said any synthetic 75w90 would work fine and suggested M1. The oil from my first drain looked pretty nasty and the M1 I just did the UOA on looked pretty bad also. I know looks don't tell the story, that's the reason for the gear lube UOA. [Cheers!]

#219676 - 07/03/03 03:16 AM Re: Mobil 1 Synthetic 75w90 gear oil
Dr. T Offline

Registered: 05/28/02
Posts: 2480
1maniac, does your 540 have a limited slip? The correct fluid is Castrol SAF-XO for non-LS/standard diff and SAF-XJ for LS applications. I know the M5's have LS, but what about the 540? If you're saying that the service manual calls for XLS, then the XJ supercedes this. I just got some XJ for my car, but haven't put it in yet. The XO is 75-90, but seems thinner than M-1 and sweeter smelling (lower sulfur??). The XJ is 75-140...thick as honey...

#219677 - 07/30/03 09:57 AM Re: Mobil 1 Synthetic 75w90 gear oil
1maniac Offline

Registered: 10/11/02
Posts: 571
Loc: Pittsburgh PA
Yep my 540i does have th elimited slip diff. Two BMW stealers swear that I only need a synthetic 75w90 and not a 140 weight. I think I'm gonna run synthetic 75w140, however. [Confused]

#219678 - 07/30/03 06:27 PM Re: Mobil 1 Synthetic 75w90 gear oil
Bror Jace Offline

Registered: 05/27/02
Posts: 5028
Loc: Saratoga, NY
Odd that Mobil 1 gear oil has no moly. Don’t most gear oils? [Confused]

I know most synchromesh fluids don’t but I assumed gear oils for diffys did. I just don’t do too much with the more traditional kinds of these fluids. [I dont know]

Anyway, the gear/tranny oils (including motorcycle oils) we have seen here (the ones I remember, of course) show about 50ppm worth of iron after anywhere from 1,500 miles to 20,000+.

Again we have a “high performance” (synthetic) fluid being used for a short interval (for the application) and then drained showing a lot of wear metals. Might the borate esters in the M1 (note the 226PPM of boron) be cleaning up the crud left behind by the old oil … which might even be the original factory fill?

I guess if I were to change the gear oil in an application which ran an extended interval, I would use a cheap, $2-per-quart fluid for a few hundred miles (maybe 1,000 – max!) and then drain again and fill with the good stuff. Adding a teaspoon of Neutra 131 or Auto-RX to the short-time stuff might not be a bad idea either.

I’ll practically guarantee that you’ll get better results from the Amsoil you’re currently running … even after a significantly increased interval. However, I’m equally confident that they won’t mean anything definite. [Frown]

--- Bror Jace

#219679 - 07/30/03 06:47 PM Re: Mobil 1 Synthetic 75w90 gear oil
MolaKule Offline

Registered: 06/05/02
Posts: 16388
Loc: Iowegia - USA

As others have pointed out, this iron reading is not really unusual for a diffy that has just run synthetic gear lubes. The esters are cleaning out residual metals from run-in.

What I have been seeing is anywhere from 200+ ppm of iron down to 35 ppm after a number of lube changes. My previous UOA's of a 75W90 diffy fluid high in esters was 225 pm now down to about 30 ppm after about 3 changeouts. I prefer not to see a TAN go over 4.0 in a used gear lube.

#219680 - 07/31/03 08:50 PM Re: Mobil 1 Synthetic 75w90 gear oil
Dr. T Offline

Registered: 05/28/02
Posts: 2480
Only M cars (M3, M5, etc) have a LS Rear diff.. Your 1994 540i should only have a standard diff. requiring the standard Castrol SAF-XO Synthetic rear lube (BMW Synthetic final drive lube).

#219681 - 08/01/03 07:19 AM Re: Mobil 1 Synthetic 75w90 gear oil
wtd Offline

Registered: 06/25/02
Posts: 1427
Loc: southwest Mo.
Here is the results from the rear end in my 98 Chevy ext-cab Z71 with the G80 locking rear. I had this analysis done last year and am still running the gear lube this sample came from. It is Mobil 1 75W-90 and had 24,099 miles on the sample. Blackstone labs did the analysis.

Aluminum 2
chromium 1
iron 116
copper 2
lead 1
tin 0
moly 0
nickel 1
manganese 18
silver 0
titanium 0
potassium 0
boron 170
silicon 10
sodium 7
calcium 11
magnesium 3
phosphorus 1726
zinc 81
barium 0

SUS viscosity@210*F 68.8
flashpoint 405
water % 0
insolubles 0.2

Blackstone said that wear read about 1/3rd average and suggested running the oil another 15,000 miles and retesting. Truck had 43,587 miles on it at time of sample and has 53,834 now.


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