black gear lube in a ford

[brian]

I have a related question. The first owner of my Jeep 4.0 changed the axle lube within a few hundred or thousand miles of factory new. He used Mobil 1 75w-90. When I drained the M1 75w-90 at 50Kmi, front and rear lube was black. I replaced the fluids with M1 75w-140 at the FSM recommendation for severe service.

What caused the M1 75w-90 to turn black? Was it the fact that the axles were still breaking in or some other reason like excessive heat?

-brian

 

[MolaKule]

It could have been heat or most likely the esters were cleaning up the inactive sulfur and crud from the diffy.

 

[brian]

But how much crud would there have been in 500-3000 miles of use?

 

[MolaKule]

The blackness or darkness of the fluid is due to the large amount and type of sulfur additive used in the factory gear lube.

I was discussing this with an additive supplier the other day and he confirmed this fact.

Moly gear lubes such as Schaeffer's #267 are very dark due to the moly's as well.

 

[slc10844]

quote:

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The blackness or darkness of the fluid is due to the large amount and type of sulfur additive used in the factory gear lube.

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Can I expect the replacement fluid to turn black also, or do they use a different formula lube during assemlby?

 

[MolaKule]

It depends on how much crud was in there and how hot the fluid became from the gear loading.