2000 Ranger 3.0 4X4 R7 ls axle code. Looks like i'm getting some good seepage at the rear diff so i'm gonna pull the cover and change the oil. Couple of questions, the manual calls for sae 80w90, not sure if it was filled with synthetic or dino from factory? I'd like to go synthetic regardless but am having a hard time finding a synthetic 80w90. Will a different spec oil work? If i run synthetic is a friction modifier still necessary? Gonna tackle this tomorrow. Thanks in advance!

 

You'll find more 75W-90 around in synthetic (or semi-syn) which is fine. Valvoline or Mobil 1 is a good bet.

 

I don't believe you need the modifier if you go Full Synthetic, not sure about the semi, yes for dino.

 

That's right, some brands might have more modifier in them than other brands (some also have no modifier).

A lot also depends on the condition of the LS clutch packs. Which is why the best way to determine how much modifier (if any) is needed is to change out the fluid and then drive around for while before you start adding any. See: https://www.ford-trucks.com/forums/3...ing-loose.html

 

I'd use Mobil 1 75w 90, I use the 75w 140 in mine.

 

Well I ended up going mobil 1 75-90 with a 7oz tube of modifier. The modifier I bought said to add the whole 7oz tube, just looked in manual and it said to only add 4oz of modifier. Probably overkill but everything seems to be working fine. Also found that the diff cover wasn't actually leaking it was coming from the pinion seal. I found that the vent tube was almost fully blocked and after it was cleaned no more leak. I had already bought the mobil 1 so I went ahead and changed it out anyway.