Lifetime is a bunk marketing gimmick IMHO. No fluid is lifetime per se. If you plan on keeping the car or truck for a significant length of time, change it out...fluid is cheap insurance. If you only plan on keeping the vehicle until it's paid off, etc, then assume it's "lifetime" and let it be.
Rear Diff Factory Fill Come Out Grey Nasty?
- Thread starter gathermewool
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I changed out the front and rear diff on my wife's car (Subaru Forester XT) at 60K. The front diff fluid flowed out like a thick oil (exactly what I was expecting), however the rear diff came out like molasses. I replaced both with Mobil 75W90.
The rear diff lube works a lot harder than the front...the rear takes the brunt of the load. My Jeep is the same way....the front lube is always in much better condition than the rear.
possibly clutch material if it has limited slip
Hmmm.
Wonder what the fluid looks like in my F150 w/ 118K on the factory fill...
Wonder what the fluid looks like in my F150 w/ 118K on the factory fill...
I'vve had grey nasty stuff come out of my outboard motor drive unit.
It's from water, and some metal wear, of course.
I suspect that perhaps condensation might be responsible for the fluids' condition.
It's from water, and some metal wear, of course.
I suspect that perhaps condensation might be responsible for the fluids' condition.
10K is the general rules for all gear related parts so transmissions,differentials generally should be let go for 10K on factory fill. It all depends on how much time was spent by the OEM hand lapping the gears in.
Some OEM use molly EP assembly lube or fluids loaded with molly in their gear lubes. I do not think that this is the case though. You never did say how many miles your gear oil has on it?
After the break in phase the old rule of thumb baring water crossings and such was 2 years or 24K miles. With the advent of synthetics a lot of people like to at least go 50K miles on a fill of synthetic gear oil.
Some OEM use molly EP assembly lube or fluids loaded with molly in their gear lubes. I do not think that this is the case though. You never did say how many miles your gear oil has on it?
After the break in phase the old rule of thumb baring water crossings and such was 2 years or 24K miles. With the advent of synthetics a lot of people like to at least go 50K miles on a fill of synthetic gear oil.
gathermewool
Site Donor 2025
The rear diff in my STI is a Torsen 2 - not a clutch type. The factory fill came out dark gray after 17kmi. It seems a lot of guys don't agree with my changing it out so early, but I feel that worst case I have better lube in there; best case I prevented excessive wear.
I sent a sample out for analysis, but nothing really popped out at me as abnormal. Here's what they found:
[censored] Comment: Maybe the fluid came out looking darker than expected because of the extra iron. We're guessing it's present because this is the factory oil, so new parts were wearing in while this oil was in place. If you run your next differential oil 17,000 miles too, wear metals should be better next time
(if our theory about iron is correct). The TAN read 2.2, so the oil is not terribly acidic. To know how acidic it has become, it helps to know where the TAN starts out. Not all oils start at 0.0. Insolubles are okay at 0.3%. No moisture found.
Al: 2
Cr: 4
Fe: 317
Cu: 1
Pb: 0
Sn: 1
Mo: 1
Ni: 47
Mn: 20
Ag: 0
Ti: 0
K: 4
B: 170
Si: 8
Na: 5
Ca: 10
Mn: 1
P: 1294
Zn: 27
Ba: 10
SUS (210F): 85.7
cSt (100C): 16.94
Flash: 405
Insolubles: 0.3
TAN: 2.2
I sent a sample out for analysis, but nothing really popped out at me as abnormal. Here's what they found:
[censored] Comment: Maybe the fluid came out looking darker than expected because of the extra iron. We're guessing it's present because this is the factory oil, so new parts were wearing in while this oil was in place. If you run your next differential oil 17,000 miles too, wear metals should be better next time
(if our theory about iron is correct). The TAN read 2.2, so the oil is not terribly acidic. To know how acidic it has become, it helps to know where the TAN starts out. Not all oils start at 0.0. Insolubles are okay at 0.3%. No moisture found.
Al: 2
Cr: 4
Fe: 317
Cu: 1
Pb: 0
Sn: 1
Mo: 1
Ni: 47
Mn: 20
Ag: 0
Ti: 0
K: 4
B: 170
Si: 8
Na: 5
Ca: 10
Mn: 1
P: 1294
Zn: 27
Ba: 10
SUS (210F): 85.7
cSt (100C): 16.94
Flash: 405
Insolubles: 0.3
TAN: 2.2
You did good to swap the FF out. I did mine at 10k miles, and wish I had done it even sooner... maybe around 5k. I ran Motul Gear 300 next for 24k, changed it again to Motul Gear 300 and will run 30k mile runs from now on.
My FF was worse looking than yours. Must be a fancier FF for the STI
What did the magnet look like?
My FF was worse looking than yours. Must be a fancier FF for the STI
What did the magnet look like?
gathermewool
Site Donor 2025
I changed mine out with Motul Gear 300 as well. The magnet had a very thin layer of muck on it the same color as the fluid. I'm still unsure what causes the oil to turn gray like that. I think I'll run this fluid out to 50kmi or so and change it out again. We'll see how long before the oil-changin finger gets itchy, though!
Originally Posted By: gathermewool
What about for a crem de la creme, boutique oil like Motul or Amsoil? If regular use diffs are going 200k+ miles then what's to say mine can't go 200k+ on a fantastic gear lube?
Go with the Amsoil SVG and run it 100k no problem. It will pay for itself. But I would change it at 100k.
What about for a crem de la creme, boutique oil like Motul or Amsoil? If regular use diffs are going 200k+ miles then what's to say mine can't go 200k+ on a fantastic gear lube?
Go with the Amsoil SVG and run it 100k no problem. It will pay for itself. But I would change it at 100k.
gathermewool
Site Donor 2025
Originally Posted By: PT1
Originally Posted By: gathermewool
What about for a crem de la creme, boutique oil like Motul or Amsoil? If regular use diffs are going 200k+ miles then what's to say mine can't go 200k+ on a fantastic gear lube?
Go with the Amsoil SVG and run it 100k no problem. It will pay for itself. But I would change it at 100k.
On paper it seems Motul is a much better lube. I hate defaulting to the I'll-change-it-early-for-peace-of-mind mentality, but that's probably what I'll end up doing in another 50k.
Originally Posted By: gathermewool
What about for a crem de la creme, boutique oil like Motul or Amsoil? If regular use diffs are going 200k+ miles then what's to say mine can't go 200k+ on a fantastic gear lube?
Go with the Amsoil SVG and run it 100k no problem. It will pay for itself. But I would change it at 100k.
On paper it seems Motul is a much better lube. I hate defaulting to the I'll-change-it-early-for-peace-of-mind mentality, but that's probably what I'll end up doing in another 50k.
Originally Posted By: gathermewool
I changed mine out with Motul Gear 300 as well. The magnet had a very thin layer of muck on it the same color as the fluid. I'm still unsure what causes the oil to turn gray like that. I think I'll run this fluid out to 50kmi or so and change it out again. We'll see how long before the oil-changin finger gets itchy, though!
Old gear oil turns gray because it has tiny iron particles suspended in it, caused by gear wear.
I call it the gray slime of death because I tend to only see bearing failures in rear axles where the stuff was never replaced.
I changed mine out with Motul Gear 300 as well. The magnet had a very thin layer of muck on it the same color as the fluid. I'm still unsure what causes the oil to turn gray like that. I think I'll run this fluid out to 50kmi or so and change it out again. We'll see how long before the oil-changin finger gets itchy, though!
Old gear oil turns gray because it has tiny iron particles suspended in it, caused by gear wear.
I call it the gray slime of death because I tend to only see bearing failures in rear axles where the stuff was never replaced.
gathermewool
Site Donor 2025
I really do appreciate every one's input on here, but I'm not so sure it's iron in the oil that's causing the discoloration. What it very well might be is a black oxide - the good kind - that is adhering to the diff surfaces, with some being held in suspension. I've seen it in chemistry-controlled fluid system, but I'm guessing when it comes to what we're seeing here. The only thing that reasons against that is when people change out a couple of times, and the fluid becomes cleaner and cleaner looking - no oxide layer forming. It just doesn't seem likely that so low a ppm Fe would cause such discoloration. Have been wrong, and I could be wrong now.
Some one asked a similar question on nasioc.com, and the thread was locked immediately after I posted about my gray fluid findings. The mod stated that every one knows that oil color has nothing to do with quality, and that we should simply follow the manufacturers recommendation - inspect at 30k and 90k.
I'm not sure if he was confusing motor oil that is filtered and exposed to combustion byproduct, water and fuel contamination, but it kind of upset me that a topic that should be open for discussion was locked so quickly.
Some one asked a similar question on nasioc.com, and the thread was locked immediately after I posted about my gray fluid findings. The mod stated that every one knows that oil color has nothing to do with quality, and that we should simply follow the manufacturers recommendation - inspect at 30k and 90k.
I'm not sure if he was confusing motor oil that is filtered and exposed to combustion byproduct, water and fuel contamination, but it kind of upset me that a topic that should be open for discussion was locked so quickly.
Yeah, some forums are manual sticklers, with little room for deviation from the matrix. You'll also find on those same forums many examples of failed diffs and transmissions from the masses.
Now, free thinkers like us have the benefit of learning past the norm, only to find how deep the rabbit hole really goes
Now, free thinkers like us have the benefit of learning past the norm, only to find how deep the rabbit hole really goes
gathermewool
Site Donor 2025
My point has always been that if there is any benefit what-so-ever in changing to a relatively cheap, $20/L gear oil then I'll do it. Also, there's a difference between my 305 CHP application and the base base Impreza's 170 CHP, but that's not reflected in the service manual. Is the FF really so robust that it can handle a potentially more severe service with out ever needing to be changed? Are they saying that the base Impreza's rear diff will outlast the car under normal driving, and the STI will maybe last 150k? These are questions I have, and the only answers I'm getting are based on speculation.
I'm also not doing this simply because I'd like peace of mind, although that is a big part of it. I'm asking for some one to definitively explain to me why the FF comes out looking so terrible, if it really corresponds with something negative. Some say it is an additive like Moly, but my UOA shows nothing to back that up. Others say it's clutch material from the LSD, but that doesn't hold up since the T-2 isn't a clutch-type LSD. There has to be something common between the earlier clutch-type LSD Subies and my newer type, and the only straw I have to grasp at so far is that it might be excessive Fe wear.
I'm also not doing this simply because I'd like peace of mind, although that is a big part of it. I'm asking for some one to definitively explain to me why the FF comes out looking so terrible, if it really corresponds with something negative. Some say it is an additive like Moly, but my UOA shows nothing to back that up. Others say it's clutch material from the LSD, but that doesn't hold up since the T-2 isn't a clutch-type LSD. There has to be something common between the earlier clutch-type LSD Subies and my newer type, and the only straw I have to grasp at so far is that it might be excessive Fe wear.
From the stuff stuck to my rear diff magnet, it's metallic alright:
http://sugar.webfors.com/gallery/gearllube/2008_11_18_004?full=1
Whatever couldn't stick to the already full magnet was floating in suspension in the fluid. Now, could there be other things contributing to the grey color... maybe. But the most obvious answer is usually the most likely one.
And this is from a NA boxer which sees almost half the power your diff sees.
http://sugar.webfors.com/gallery/gearllube/2008_11_18_004?full=1
Whatever couldn't stick to the already full magnet was floating in suspension in the fluid. Now, could there be other things contributing to the grey color... maybe. But the most obvious answer is usually the most likely one.
And this is from a NA boxer which sees almost half the power your diff sees.
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