Is it possible to determine if differential fluid is losing efficacy?
What is the measure? Viscocity? Can efficacy be quantified easily?
Actually I would be interested in knowing if there are quantifiable
measures for the efficacy of other fluids, assuming they are not
contaminated or burnt. Thank you.

P.S. I changed the front and rear differentail fluids in my Jeep WJ
2004, AWD, first time after 50K miles. I saw that the old fluid was
quite viscous, only slight brownish, not horribly bad smelling, and
did not seem to have any metal shavings. I am starting to wonder if I
could have done the change after a few more 10K miles...

If they are limited slip differentials you want to follow the change
intervals religiously. If they are not the fluid may last the life of the
vehicle---but who wants to take chances?

I would recommend synthetic next time, to cut down on friction losses in the
winter. This is one place where synthetic might be economically viable.

In addition to viscosity you care about something called "shear strength",
which is a function of additives. I don't know how you would determine that
in used differential oil. You also care about water contamination. If you
even suspect that you put the rear axle under water, at least check it for
milkshake consistency. If it rains a lot where you are, level and
consistency checks should be somewhat more frequent.

Cheers,

Earle

"stilllearning" <shahswim (AT) yahoo (DOT) com> wrote