Rear Differential Fluid-- Conventional or Synthetic At This Point | Ford Explorer Forums - Serious Explorations

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Rear Differential Fluid-- Conventional or Synthetic At This Point


Active Member
May 11, 2014
Reaction score
City, State
New Mexico
Year, Model & Trim Level
2005 Ford Explorer

After searching on this site and reading these threads along with one or two others:

I was going to change the rear differential fluid as I am probably overdue. I have 167,x.. on the car. I changed the rear diff fluid at 130,x.. miles but I cannot remember if I used synthetic or conventional. At this point does it make a difference? One of these thread states synthetic is called for in the rear differential. If it does have conventional and I go with synthetic do I risk leaks? I have the 3.55 open differential so I know I do not need a friction additive the limited slip models do.

Or, is this just one of those topic we tend to overthink and just getting it done is what is most important?


I might have answered my own question. In looking at the housing it is clearly stamped "synthetic fluid" so I am 99% positive that would have been what I used.

The front is specked Dino, but the rear is Syn. There's a service pointer to add more fluid and fill from the top at the speed sensor..
If the rear diff takes 2.5 quarts, you add the rest of the last quart for a total of 3..
I used Amsoil 75/140. Even with the thicker oil, the original dirty oil ran quiet. The clean oil was noticeably louder for a while but has since gotten quiet..