Royal Purple 75W-140 Gear Oil after 50k miles?

[BruceM]

Was doing the axle seals on my truck today and while doing them I was suprised to see the small amount of gear oil loss come out in a sort of grey color. I had filled the rear diff bout 4 years ago, with Royal Purple 75w-140 gear oil, and I was a little concerned by the color. I pulled the plug to check the fluid level and it is a tiny bit below the hole, but my axle seals have prolly been leaking for a while. Also the magnetic plug really didn't have all that much of a metal coating on it, which kinda gave me the impression that perhaps all was well with the fluid and it just naturally takes on that color with age/use.

Anyone ever cracked open a Royal Purple filled differential and made note of the oil color as it drained. I've seen various colors from other vehicles, but I've never knowingly seen royal purple being drained as to tell if it's normal.

If I weren't unemployed for the past 1.5 years I wouldn't hesitate to spend the $60 bucks and change the oil, but I can't justify the expense if the oil is fine. Later on I can link a picture of a bit of the oil I caught in a plastic cap.

 

[oldhp]

I saw it in my 03' Dakota after 50K or so miles. I drained and refilled with RP 75W90 at 1K to get any metal that rear end made. The fluid drained clean, but there was a fine coating of gray slime on bottom of differential housing, wiped out with one rag and was only on the bottom. No metal filings/chips and gears looked perfect. No noise with it either. Put RP 75W90 back in it. When I sold it at 122K, no noise or issues. Truck is still running around here.

 

[Clevy]

I've used RP in the past however once I discovered red line I'm not looking back.

 

[Rand]

Not really bashing RP but their gear oil is not one of my favorite products. Its also not as buffered as some other brands and is unsuitable for MT (or anything with yellow metal) use.


I'd pick redline, amsoil, m1 and several other brands first..
esp. at their price.

I'd probably change it. 50k miles is long enough.

 

[BruceM]

Well from looking at it in the light of the sun it isn't really grey like I thought originally. Its kind of a purplish red that just looked off to me when it first came out. Also this was what came out of the wheel hub in the rear of the truck so I am betting it dosen't really flush out all that much when under normal driving.

I was looking at Amsoil, and noticed that their Severe Gear 75w140 is spec'd at 100k for normal conditions and 50k for "severe" conditions. given that I do tow heavy [censored] occasionally, drive around with 80 gallons of vegetable oil in the bed, 6in lift, 37in tires, and have submerged my axles a couple of times (hurricane Irene and a few fun creek crossings) I guess I could consider my truck for the severe schedule. So if Amsoil say 50k for thier gear oil, I'm gonna bet Royal Purple would be around the same (even though they don't list intervals anywhere).

So it appears that I'll be changing the oil, I am planning on Mobil 1 from Advance. 4qts (really 3.5-3.6qts needed) with discount code will come out round $14.50 or so a quart. I guess it's not all that bad, and I should be good to 260K+.