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97 Legacy OutBack, 09 Forester XT, 12 Silverado 2500HD
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Discussion Starter #1
I have ran several brands of fluid in this car of the years...started with PZ 75w90 at 50k, changed to RP 75w90 around 100k, changed to Schaeffer 167 75w140 last night at 166k. I used the Schaeffer for no other reason than because I had it laying around, and I had asked the question before about 75w140 and others had indicated using it without issue.

Both the PZ and the RP drained looking bad, but there was very little debris on the magnets either time...each of these drained like water too (sheared?). The RP still felt good, albeit very dirty (black). I decided to drain last night because I have felt like the car was dragging and I have been hearing more and more differential noises as of late.

Two things were very apparent right away: less noise from the differentials and much smoother/freer (it will actually speed up coasting downhill now). Took it on my daily 50 mile commute this AM, no notable difference in mileage, but I will need to fill it tomorrow to know for sure. I figure it will take a hit in the winter, but it doesn't seem to make a difference now.

I guess I was expecting a noticeable drag, poorer mileage, etc. because of the thicker lube, so I'm pleasantly surprised. I'm guessing these differentials are hard on fluid because of their small ring diameter (more loading than a large ring) and the small capacity of fluid??
 

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96 Legacy OBW, EJ22 swap, 2" suspension lift, 215/75r15, HIDs, 06 WRX interior swap
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i feel your fluid is breaking down way too fast. gear oil in most cases should be good for 80-100k and shouldnt be pitch black even then.

is you car AT or MT? if its AT could there be tranny fluid contamination which could look black and would definitely thin out gear oil.

i do mine every 50k just cause and its an amber color at its worst.
 

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Even at 180K when I changed the gear oil after 80K run it was showing a golden brown color and still transparent - though not really the same weight as the fresh stuff going in.
 

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I noted a reference to "magnets" (plural) so I presume the car is AT, with two differentials, front and rear. If that's the case, was the fluid "black" in both, or only one, and if the latter, which? If the rear, does the car have a LSD?

I ask because I've been changing the front and rear differentials on my 07 annually, and have noted that the front fluid drains with a honey color similar to when new. However, the rear always comes out noticeably darker. I've been attributing the darkness to the fact that I have a LSD, and the dark material is from the rubber seals between the differential case and the viscous-coupler's plates and fluid. Perhaps I'm wrong; some comparisons might be helpful, and might help explain steved's observations.
 

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Plain - I would also suspect more debri finding its way to the breather on the rear diff vs the front which could also contribute to this.
 

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97 Legacy OutBack, 09 Forester XT, 12 Silverado 2500HD
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Discussion Starter #7
Its a 97 and auto, so two differentials and no LSD.

Both ends drained the same. I always keep an eye on the front differential just in case the auto does leak (seen that happen in an 89 XT6), the level was consistent.

Keep in mind, RP starts out dark purple but this (while still somewhat clear on draining) was black in the pan (and you could see particles entrained in the fluid). The car sees nothing but highway, sustained high speeds at times (sometimes running 85mph+ for better than 20 miles at a shot); but all highway nonetheless. I think it was just the RP oxidizing/failing from the high speed stuff after thinking about it. If it was dirt contamination, I would have expected the magnet to show more wear metals?

The difference in driveability between the 75w90 and 75w140 is amazing though...I would not have expected the car to drive better with a thicker fluid.
 

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Plain - I would also suspect more debri finding its way to the breather on the rear diff vs the front which could also contribute to this.
Yes, very possible.

Because the vent is just at the top of the rear cover, it's going to be in the air flow around the differential, with it's high level of road dust etc. However, in order for the dust (or whatever it is) to get inside, there would have to be a pressure difference between the interior of the differential and the outside. (The vent tube is capped.) I wonder if this would be the case. There might be some air transfer due to heating and cooling, but would this be sufficient? Perhaps.

If this is a factor, wouldn't pretty well all rear differentials exhibit noticeably darker-colored gear oil when drained, which is what steved reported? (What do you do to have golden colored oil drain out after 80k?)
 

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Yes, very possible.

Because the vent is just at the top of the rear cover, it's going to be in the air flow around the differential, with it's high level of road dust etc. However, in order for the dust (or whatever it is) to get inside, there would have to be a pressure difference between the interior of the differential and the outside. (The vent tube is capped.) I wonder if this would be the case. There might be some air transfer due to heating and cooling, but would this be sufficient? Perhaps.

If this is a factor, wouldn't pretty well all rear differentials exhibit noticeably darker-colored gear oil when drained, which is what steved reported? (What do you do to have golden colored oil drain out after 80k?)
Front was golden - just a few shades darker than the new stuff and a tad thinner of course. The rear I recall being darker but not by a large margin. It is a CA car which might see less water and road grime exposure via fewer extreme winter road miles etc.
 

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2011 Tacoma TRD Sport Double Cab Long Box
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I don't think either of mine had ever been drained when I bought it, and at ~110-115k, neither were anywhere near black. There was a little bit of sludge on the magnet on the front diff, but nothing crazy.

Both were thinner than the new oil, but the color wasn't all that much darker. At first I thought the rear was really bad when I drained it, but it was the container I drained it into tricking me!
 

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Keep in mind, RP starts out dark purple but this (while still somewhat clear on draining) was black in the pan (and you could see particles entrained in the fluid).
I misunderstood -- I thought the oil was dark each time it had been changed, but on re-reading the text, I now appreciate that the "black" was only in reference to the used RP, which, as noted, does start out darker.

I have a number of clear, calibrated, plastic measuring cups (dollar store) that I use to examine the color, and compare the oil drained from the two differentials as well as new fluid each time the fluid is changed.

I'll be changing the differentials again in a few weeks and will try to take (and post) some photos that show the differences. Perhaps we're using different terms (dark, black) for essentially the same thing.
 

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97 Legacy OutBack, 09 Forester XT, 12 Silverado 2500HD
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Discussion Starter #14
Perhaps we're using different terms (dark, black) for essentially the same thing.

Possible.

It still had "stuff" in it, which didn't seem to affect the wear; but it was definitely there and not normal. I did not expect the fluid to drain like it did...again, RP is a dark purple, and I know it loses its purple color after some time in use; but it typically turns a "gear oil" brown, not black and not with particles in it. Again, I would wonder if the particles were oxidation remnants?

Not sure whether RP is any good, it seems there are lovers and haters of the stuff. It was obviously hurt, and its not like a NA OBW is putting any huge stress on things?
 

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"stuff" in it, which didn't seem to affect the wear; but it was definitely there and not normal.
I would tend to focus more on the particles rather than the color -- whether the particles are soft, e.g. some sort of gum formed by the oil (probably not of great concern, but suggests more frequent changes) or hard, metallic pieces. If metallic, size would be the next parameter. It's not unusual for very tiny dust-size material to be found -- the gears do mesh and wear, as is evident from the patterns on the teeth even in a properly running differential -- and so some metal material might be evident.

One sort of test I've done is to strain the oil through a paper coffee filter. The tiny wear particles will darken the paper, but won't be individually visible, whereas larger "chunks" will.

I would wonder if the particles were oxidation remnants?
Are you referring to oxidation of the RP, or the metals? I suspect the RP. (No reason for the metals to oxidize/rust unless the car was parked for a long time or water was collecting inside.) If so, then perhaps it's not up to the task, or at least the oil change interval, assuming there weren't any unusual situations, such as frequent spinning of one wheel.

All speculation at this point. I suppose the definitive answer might come from having the fluid analyzed by a lab (e.g. Blackstone).
 

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97 Legacy OutBack, 09 Forester XT, 12 Silverado 2500HD
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Discussion Starter #16
There were no visible metallic particles in the oil, and almost nothing on either magnet.

The stuff floating around looks like soot or carbon for lack of a better description. The reason I wondered if it was something from the lube itself...this car very rarely sits, and I would have expected the stuff to have been well blended by the gear set; but it wasn't. I have never seen gear oil look this way before, the reason I noted it...it definitely wasn't metallic, and it likely isn't seals as neither differential leaks.

This is the fourth change of fluid in this car...the first was OE oil to about 50k, then PZ to about 85k, then two hits of RP 75w90 between the 85k mark and 166k. This fill of RP looked completely different than the previous, and had it looked different between the two differential units; I would have suspected contamination. I suspect I may have gotten a bad lot of oil (which isn't the first I have gotten from RP, and the reason I no longer use their stuff).
 

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I dunno about Royal Purple, but Redline LightWeight Shockproof (and the other weights I guess) very purposefully has particles suspended in it. They are part of the technology used for lubrication/protection of gear surfaces. In fact, they explain the product should never be used in an application that has a pump/filter.

Anything floating in the fluid where the magnets are clean is either aluminum or rubber/seal material or some other non-ferrous 'slime'/carbon.
 

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97 Legacy OutBack, 09 Forester XT, 12 Silverado 2500HD
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Discussion Starter #18
I dunno about Royal Purple, but Redline LightWeight Shockproof (and the other weights I guess) very purposefully has particles suspended in it. They are part of the technology used for lubrication/protection of gear surfaces. In fact, they explain the product should never be used in an application that has a pump/filter.

Anything floating in the fluid where the magnets are clean is either aluminum or rubber/seal material or some other non-ferrous 'slime'/carbon.

Yeah, Schaeffers has molybdenum that will settle out (ask me how I know that!), but I don't think RP has anything like that.

That's the reason I think its something from the degradation of the RP, nothing else fits...it would be too coincidental to have seals/rubber material at both ends, not to mention it didn't happen with the last fill of RP (the last fill drained purple and clear).
 
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