Can Friction Modifier Change the Color of Gear Oil?

[Exproblems]

Nearly 3 years ago or 14,000 miles of driving, I changed the Rear Differential gear fluid in my 2005 Ford Explorer. Back then I installed Mobil 1 75W-140 Full Synthetic gear oil and added a tube of Friction Modifier that I bought from Advance Auto Parts.. While checking the fluid level yesterday on the Rear diff, I noticed the color of the rear diff fluid was very dark in color, almost black looking. The rear diff was full of fluid and I am not having issues with the rear diff. I was just wondering if the Friction Modifier I added could cause a darkening effect on the gear oil, does anyone know this to be true? Thanks for any help!

 

[Donystoy]

Any gear oil is usually very dark in color especially when it has been in use for some time. It is when it looks like aluminum paint that you have to worry.

 

[Exproblems]

Any gear oil is usually very dark in color especially when it has been in use for some time. It is when it looks like aluminum paint that you have to worry.

Okay thanks. Aluminum or silver in color would mean metal flakes in the gear oil?

 

[wvex100]

most of the friction stuff is moly which is almost black. the oil is amber so it would turn very dark when mixed
and yes the silver would be metal

 

[Exproblems]

most of the friction stuff is moly which is almost black. the oil is amber so it would turn very dark when mixed
and yes the silver would be metal

Thanks for the info on Black Moly! Not to be confused with the "Black Molly's" aka "speed" back in the 70's and 80's.

 

[Donystoy]

most of the friction stuff is moly which is almost black. the oil is amber so it would turn very dark when mixed
and yes the silver would be metal

Just wondering, The only friction modifier that I have ever purchased was from the Ford dealer for 9" locker rear ends used in older Fords. It was always blue in color. I might have to work on the rear end on my Explorer as well soon and was wondering if there are different types of modifiers for different applications or years of vehicles. Are some designed for use with synthetic gear oil and others for standard gear oil?

 

[wvex100]

that blue stuff was some kind special oil that was used in the Detroit lockers. I had one in 78 chevy and it had a special oil. with odd smell. I dont think it was ANTI friction. c
The directions said to make sure ALL the gear oil was cleaned off.

 

[Donystoy]

It was definitely a friction modifier. I had an Auburn locker installed by my transmission shop and was almost thrown into the ditch when it grabbed going around a slight curve while going down a hill. Gave the shop a call and was told that I "might" have to add some friction modifier into it. After I put it in it ended that problem. It came in a small 5oz bottle.
I went to Auburn web site where it said that friction modifier "must" be added.
Am I correct in assuming that if the rear differential on my Explorer is an open one that modifier is not required?

 

[Exproblems]

Am I correct in assuming that if the rear differential on my Explorer is an open one that modifier is not required?

You are correct! Friction Modifier is only needed with a "Limited Slip" diff, not in "Open Diff's".

 

[Donystoy]

Thanks. I have to replace the axle seals as they are leaking. I only have around 80,000 miles on the vehicle and this will be the second time. It was only two years old when I purchased it and paid $100 to have the original owners gold extended warranty transferred to me. Because of this the original seal replacement was under warranty. Best $100 I ever paid.
I wonder how many Explorer rear ends get destroyed due to lack of oil from these poor quality seals. If you always park on a gravel driveway you would not be aware of a leak.