08 Ranger - Pick my next differential fluid

Joined
Dec 23, 2020
Messages
367
Location
Midwest
I'm planning on changing out the dif fluid in my teen son's truck in the next couple of months. It's a 7.5 inch 3.73 limited slip. Choices:
1) Motorcraft 80W-90 with Motorcraft friction modifier
2) Castrol Limited Slip 80W-90 (assuming it has friction modifer pre-mixed in)
3) Motorcraft 75W-90 Synthetic (do I still need friction modifier?)
4) some other recommendation

We purchased this truck a few thousand miles ago and have no idea when or if the differential fluid was ever changed. Currently has 190k miles. I'd like a high quality synthetic that we may never change again (I say that because it's driven ~5k miles per year and given a normal 30k fluid change interval, we may not have the truck after 30k miles), but only if it makes sense. Does regular Motorcraft+friction modifer make the most sense? Opinions?
 

BlueOvalFitter

Site Donor 2021
Joined
Feb 28, 2003
Messages
10,487
Location
Cajun Country, La.
I'm planning on changing out the dif fluid in my teen son's truck in the next couple of months. It's a 7.5 inch 3.73 limited slip. Choices:
1) Motorcraft 80W-90 with Motorcraft friction modifier
2) Castrol Limited Slip 80W-90 (assuming it has friction modifer pre-mixed in)
3) Motorcraft 75W-90 Synthetic (do I still need friction modifier?)
4) some other recommendation

We purchased this truck a few thousand miles ago and have no idea when or if the differential fluid was ever changed. Currently has 190k miles. I'd like a high quality synthetic that we may never change again (I say that because it's driven ~5k miles per year and given a normal 30k fluid change interval, we may not have the truck after 30k miles), but only if it makes sense. Does regular Motorcraft+friction modifer make the most sense? Opinions?
The correct weight that is spec'd for the differential. And, friction modifier, if needed.
Even if the differential fluid states there is FM in it, add FM anyway!
 

himemsys

Thread starter
Joined
Dec 23, 2020
Messages
367
Location
Midwest
The correct weight that is spec'd for the differential. And, friction modifier, if needed.
The spec'd oil is 80W-90 Motorcraft with Motorcraft friction modifer -- the first option in my list. I'm intrigued by the Supertech 75W-90 Synthetic, though.
 
Joined
Mar 20, 2008
Messages
12,521
Location
USA
Another vote for Walmart's ST Synthetic 75w90.

If you don't have a pump to refill the diff with, Valvoline has a quart of gear oil in a pouch/bag that can make it easier to fill with. It is also available at Walmart.
 
Joined
Aug 20, 2003
Messages
16,755
Location
NE,Ohio
The spec'd oil is 80W-90 Motorcraft with Motorcraft friction modifer -- the first option in my list. I'm intrigued by the Supertech 75W-90 Synthetic, though.
most likely the clutches in the "limited slip" are totally toasted and need rebuilt.

Use the least amount of FM you can so the limited slip might actually do something. too much FM= too much slipping. Too little and you will get some chattering/noises if they arent worn out.
 
Joined
May 21, 2018
Messages
2,690
Location
South Carolina
I'm quite pleased with the SuperTech Synthetic 75w-140 in ALL my vehicles. When did Ford go back to 80w-90? When Ford warranty rebuilt my Ranger rear axle they installed 75w-140. Mechanic said all RWD's were spec'd for 75w-140 now. I looked up the TSB and he was right. Wish I could find that TSB now!
 
Joined
Aug 10, 2020
Messages
8,060
Location
Roanoke Virginia
This will be a shocker to most but another vote for SuperTech from me. Ever since my friend used it twice and it didn’t do anything to his car I trust it again now. Maybe it was a bad batch my customer got a hold of.
 
Joined
Apr 30, 2019
Messages
505
Location
kansas
When i had a 94 b4000 it ran supertech 75w90 in the rear diff and for awhile supertech dex/merc in the transmission and both were working great when i hit a deer and totaled it.
 

01rangerxl

Site Donor 2021
Joined
Apr 8, 2006
Messages
10,527
Location
Birmingham, AL
My 2002 Ranger with an open 3.73 7.5 has lived most of its life with synthetic 75w90. I changed the original 80w90 with Mobil 1 75w90 around 50k, changed it again with store brand synthetic 75w90 maybe around 160k when the cover leaked, then again at 215k or so when I did the rear axle seals and outer bearings. Don't plan to change it again unless I have to remove the cover for something else. There's over 250k on it now and the truck is not babied. If it starts spinning going up the driveway I just gun it and one wheel peel to the top. 🤣
 
Joined
Aug 12, 2013
Messages
1,070
Location
Alberta
1617253355494.jpeg
 
Top