[steved]

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??

 

[steved]

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.

 

[steved]

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?

 

[steved]

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).

 

[steved]

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).