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  1. #11
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    I respectfully disagree astro.
    The ability for the fluid to not lose it's viscosity ( aka shear which is a byproduct of oxidation-amongst other components ) is interlinked with the chemical components that create the viscosity.
    All things being equal...That is to say that a 75-140 will remain more resistant to oxidation than 75w-90.
    http://www.machinerylubrication.com/...ture-stability

    "Fluid exposed to high temperature can experience permanent deterioration. For example, a substantial reduction in fluid viscosity normally accompanies asperity contacts (mechanical rubbing) and an increase in temperature. In addition, irreversible viscosity change can also occur when a fluid having poor shear stability encounters high temperature. Whether through rapid oil oxidation promoted by high temperature with its accompanying sludge formation production, or simply accelerated component wear, the influence of high temperature on oil properties is serious and generally deserves prompt consideration and attention"


    "The oil might lose its ability to lubricate if its viscosity changes significantly or if it is oxidized. The manufacturing tolerance on viscosity is plus or minus 10 percent. Therefore, ISO VG 320 oil should have a viscosity that falls within the range of 288 to 352 centistokes at 40 degrees C.

    There are many possible causes for an increase or decrease in viscosity. For example, some oils have additives known as viscosity-index (VI) improvers that might not be shear stable. With time in service, these oils lose viscosity because the VI improvers shear down"


    http://www.machinerylubrication.com/...-gear-failures
    In addition, overheating might cause oxidation. Contamination by water and wear debris accelerates oxidation. The following symptoms are indicative of oxidation"

    Given the location of the angle gear and it's small capacity for oil...Plus Ford's spec of 75w-140 in their cross-overs that use an angle gear...I don't feel uncomfortable using 75w-140.
    Considering the failure mode of the Angle Gear and it's proximaty to the catalytic converter...I would rather try a preventive/ productive approach than wait for the common Angle Gear "reseal".

    OEM's are under enormous pressure to meet MPG guidelines set fourth by the EPA...it's not uncommon for auto manufacturers to make lube choices at the expense of long term durability. Aka Striebeck curve-engine under full load results in increased wear when utilizing many an OEM's oil recommendation.


    "Going heavier in grade isn't always "better". This is effectively splash lubricated. So, thinner might be better given the size and load on this assembly"

    I agree with this statement, though in this application and design; I feel it's the most effective solution from a preventive standpoint.
    Last edited by Iroll_; 12-01-2015 at 01:27 PM.

  2. #12
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    Engaging!

    Volvo recommends 90 for angle gear, however 140 grade presents characteristics that makes it work longer in hotter conditions. Would you say 140 would be a better choice for JRL, where 90 would still perform best in cooler temp areas - rest of us? LoL!

    Was the fluid ever replaced after the o'ring vtl? what fluid?
    2001 V70XC +204k miles/ XeMODeX/ Pirelli 12/32"/ Duracell 48/ MOBIL-3309/ Pennzoil EURO 5W-40/ Great Lakes

  3. #13
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    Considering that the regs for how viscosity' are classified; 75w-140 is only more viscous than 75w-90 at cold tempatures-but only slightly( this is called ktns). The real benefits of the "140" part are it's resistants to physical/mechanical shocks ( think of being stuck in the snow on a hill with a heavy load) and heat. The angle gear is always "on" so I don't feel concerned about the fluid not getting to temp or under cooling for MY application.
    24 mile commute-round trip. Lots of hills and free way driving at 60mph.
    If my conditions were flat...I would stick be more inclined to stick with 75w-90.
    Considering the design brief of the xc' the 140' adds a margin of over-engineer that gives me peace.
    Seattle has terrain that's similar to San Fran...lots of hills.

    Also like to note that the oil capacity in the angle gear is amoungst the smallest I have encountered on a "transfer case".
    On other family members cars - the awd systems in Lexus suv and car carry two or more quarts...they don't have awd "leaks" and use a non synthetic away from a catalytic converter-just a thought !

    Good luck!

    For reference-I have two thousand miles on my 75w-140 fluid in my angle gear...I'll report back on my findings.
    Last edited by Iroll_; 12-01-2015 at 08:01 AM.

  4. #14
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    OK...lots of information here...some of it inherently contradictory...some of it outright wrong...

    Let's start with viscosity specifications.

    An oil can't be the same at operating temperature and then provide a thicker film. In fact, what you said here, "75w-140 is only more viscous than 75w-90 at cold tempatures-but only slightly( this is called ktns)" is, in fact, completely backwards. The -140 has to meet a higher viscosity at 100C than the -90. That's what the numbers mean. You're even claiming that the higher viscosity offers "better shock resistance"...but if they're the same at operating temperature, that couldn't be true.

    The 75-90 and the 75-140 are similar at cold temperatures. The "W" portion of any multi-grade stands for "winter" and specifies flow characteristics at low temperature. Those temperatures vary for 0W, 5W, 10W and 15W but the principle is the same. The reason that the 75W-140 has a higher number is that it is thicker at 100C, that is, operating temperature than the -90. It's important to understand that all oils thin out with increased temperature, but a 140 has thinned out less than a 90. It's also important to understand that gear oils don't use the same scale as motor oils, so a 75W90 is pretty close in viscosity to a 10W40.

    That change in range of thickness in the 75W140 is achieved through the use of polymer additives that add thickness at high temperature. They're long chain molecules that resist flow a bit at higher temperature. The 75W90 and the 75W140 have similar base oils and similar cold performance. The hot performance is improved through these additives known as Viscosity Index Improvers. In fact, it's the VIIs themselves that are prone to oxidation and breakdown with time.

    Further, it's the VIIs that shear quickly, not the base stock, so 75W140 is inherently more prone to shear than the 75W90. That's why very high horsepower cars (like a 500+ HP V-12) specify a 80W90 in the differential. That near mono-grade rating is more shear stable, because it uses no VII. That means it stands up better to the extreme pressures with high power/torque drive trains.

    Finally, when comparing synthetic with conventional oil, it's important to understand terms. Synthetic in the US means oil that has been hydrocracked to a more precise degree (group III) as well as oils that have been built up from simple hydrocarbon (like Pennzoil's Gas to Liquid process for their Ultra line) or Poly-alpha-olefin (group V) stocks. So, with a more consistent base stock in the oil, synthetic is more shear stable, shows a more consistent grade, and offers better low temperature performance.

    So, in your transfer case (angle gear), I agree that a synthetic is the better choice over conventional. Better still is one that is changed often. Best is one that meets the original specification, without all the extra VIIs that may actually be causing the very problem that you're trying to avoid. Read your own words about the risks of VII and the cause of viscosity breakdown.

    If you're interested in more reading, start here: http://www.tribology-abc.com/abc/viscosity.htm

    And then join this site: www.bobistheoilguy.com

    As far as what Ford specifies - really, who cares? It's a differential either way... My Expedition specified 75W140 in the differential...but it was specifying a synthetic...and it was rated to tow over 9,000 lbs. Different beast altogether. The MB S600 is pushing nearly twice the power and nearly twice the torque...and it specifies an 80W90. Ask yourself why the higher load, higher power car specifies an oil with the lowest possible VII content.

    You're simply guessing that Volvo specified the 75W90 for fuel economy. But there is no proof to substantiate that as Volvo's reason. A very good oil choice for this angle gear is Mobil 1 75W90. Full synthetic. $11/QT. Meets all the specs. And at that price, you can afford to change it regularly. I've got nearly 200K on the original angle gear. No leaks, no issues. It's got Mobil 1 75W90 in it and I change it every 30,000 miles. Perhaps a bit too frequently...but getting the old oil out after exposure to all that heat is as important as choosing the correct oil in the first place.
    Current Fleet:
    2016 Tundra Crewmax 4WD 1794
    2005 MB S600 (126K, Michelin AS4, HPL 0W40)
    2005 MB SL600 (55K Michelin AS4, Mobil 1 0W40)
    2004 V70R (143K, six speed M66, HPL 5W40)
    2004 XC90 (235K, HPL 0W30 Euro)
    2002 V70-XC (295K, HPL 0W30 Euro)
    2002 V70-T5 (225K, IPD bars, Bilsteins)
    2001 V70-T5 (125K, IPD downpipe, cat back and other mods)
    1932 Packard Sedan (straight 8, dual sidemounts, original paint and interior, Shell Rotella 15W40)

  5. #15
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    Thank you for the feedback and helping to determine what is best in my situation.

    The existing/old fluid is Volvo's synthetic 75W90.

    Replacing o'ring and seals will take some effort and time -- the axle will have to come out.

    For $11, I will drain and fill with Mobil 1 75W-140 to see if it makes any difference. If 75W-140 escapes too, then the issue is more than the oil grade.

    I will also go ahead and order three items 3, 12, and 15 from Volvo for next steps.

    Many thanks.
    2001 V70XC +204k miles/ XeMODeX/ Pirelli 12/32"/ Duracell 48/ MOBIL-3309/ Pennzoil EURO 5W-40/ Great Lakes

  6. #16
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    Astor, I see your technical points but feel we're splitting hairs here.
    Bottom line is this:
    •Volvo Angle Gear's can and more often than not-have issues.
    • A reputable company that utilizes a similar design spec's 90-140 and to change it often as 20k in severe service.
    •A family friend that's a chemical engineer and lead R/D director for a state owned oil company in Latin America agee's with my methodology for switching to 75-140.

    My guess regarding the use of 75w-90 is a guess based on how these angle gears leak or howl eventually...So there is some methodology to my switch.

    "Further, it's the VIIs that shear quickly, not the base stock, so 75W140 is inherently more prone to shear than the 75W90. That's why very high horsepower cars (like a 500+ HP V-12) specify a 80W90 in the differential. That near mono-grade rating is more shear stable, because it uses no VII. That means it stands up better to the extreme pressures with high power/torque drive trains"
    This depends on the application...M3 makes 400 plus hp and spec's a 140 weight...My aunts CL600 carries a lot more diff oil than my angle gear does...Different design specs.

    Either way; I will happily serve as a test bed to see the long term effects of using 75w-140...As we have plenty of documented effects of 75w-90.
    I also added Lubro Molly For Gears MOS2-another 'no-no' by Volvo...A decision I made based on the working characteristics of MOS2.

    The OP's rational is spot-on with mine...The cost to replace the seal is much more than trying different fluid.
    Last edited by Iroll_; 12-02-2015 at 01:34 PM.

  7. #17
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    Oh, I completely agree that we're splitting hairs...but as the subject came up...I thought it a chance to discuss the finer points...and if you've seen my oil rant thread, you'll know that I'm a bit of an oil geek...

    I think that the key to longevity in the angle gear is:

    1. good fluid
    2. changed regularly

    Any owner following those two recommendations will be well served.

    Cheers,
    Astro
    Current Fleet:
    2016 Tundra Crewmax 4WD 1794
    2005 MB S600 (126K, Michelin AS4, HPL 0W40)
    2005 MB SL600 (55K Michelin AS4, Mobil 1 0W40)
    2004 V70R (143K, six speed M66, HPL 5W40)
    2004 XC90 (235K, HPL 0W30 Euro)
    2002 V70-XC (295K, HPL 0W30 Euro)
    2002 V70-T5 (225K, IPD bars, Bilsteins)
    2001 V70-T5 (125K, IPD downpipe, cat back and other mods)
    1932 Packard Sedan (straight 8, dual sidemounts, original paint and interior, Shell Rotella 15W40)

  8. #18
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    Thinking ahead... does the o'ring go over the adjusting nut... like the o'ring over the black oil filter screw-on cap.

    Here is a photo, notice a ring past the teeth...
    2001 V70XC +204k miles/ XeMODeX/ Pirelli 12/32"/ Duracell 48/ MOBIL-3309/ Pennzoil EURO 5W-40/ Great Lakes

  9. #19
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    Took little time to clean and to confirm the two seals are not leaking. Picked up seals, and o'ring from local Volvo incase the new fluid decides to escape too. It will be a bigger job.

    Drained and refilled 640ml. The suspected fluid leak and trail is now chalked for tracking.

    Old fluid was colored like coffee. New 75W140 (USD20) has same tone as Pennzoil 5W30.

    Thank you Iroll and Astro for support.

    Happy Holidays!
    2001 V70XC +204k miles/ XeMODeX/ Pirelli 12/32"/ Duracell 48/ MOBIL-3309/ Pennzoil EURO 5W-40/ Great Lakes

  10. #20
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    Quote Originally Posted by Astro14 View Post
    Oh, I completely agree that we're splitting hairs...but as the subject came up...I thought it a chance to discuss the finer points...and if you've seen my oil rant thread, you'll know that I'm a bit of an oil geek...

    I think that the key to longevity in the angle gear is:

    1. good fluid
    2. changed regularly

    Any owner following those two recommendations will be well served.

    Cheers,
    Astro
    Cannot go wrong with this.


    I am hoping to prolong changes with the 75w-140. I plan on taking before and after IR readings plus an analysis to get some more data-points; ( many of which fly over my head, so I heed console to those that are wiser than I).
    I Look forward to presenting the data.
    To the OP, I used Amsoil Severe Gear 75w-140...Since it's what was available locally...Come to find out-Mobil is a large supplier to Amsoil....Had Mobil been available locally, I would have gone that route.

    Xheart....With the new fluid...What are your thoughts (if any) on the XC's drivability?

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