mn_f150

Truck is a 2005 F150 Lariet with a 5.4 L engine and a standard transmission (no LS). Axle code is 26...

I am planning on changing the rear differential oil in the truck.

Question on the rear differential oil to use. The owners manual says to use 75W-140 for the rear differential. However, I just talked to a Ford Service shop rep that "I trust" and Ford recommends putting in a 80W-90 instead. They (this shop) has seen issues with bearings going out in the rear end for trucks that drive high speed miles (70 mph) speeds with a load, and their Ford Rep has indicated that the oil should be 80W-90 vs. the 75W-140 in the owners manual. Since they have switched, they have not seen the problem since.

So, should I go with 75W-140 or 80W-90 in the rear differential? Any words of wisdom here?

Thanks in advance!

techrep

iTrader: (1)

Mobile 1 80-90W

mn_f150

Since I am an Amsoil guy, would go with their 80W-90. :-)

techrep

iTrader: (1)

Then why you asking....

mn_f150

Oops, sorry for the flippant reply.

Truly trying to understand if folks' experience say stick with 75W-140 or move over to 80W-90. I had purchased the 75W-140 but based on conversations today I will most likely return it and put in 80W-90.

In a very short period of time, I have come to appreciate the "experience" that is shared in this forum.

Thanks again for the "experienced" advice that everyone is sharing.......

otto457

The only problem with the 9.75 is the limited slip clutches like to fail if friction modifier isn't used correctly. You don't have to worry about that. The early 04's had some bearing issues, but those were isolated incidences. You can use either oil with confidence, I like a higher VI oil but that's just me. If you're really worried about the diff, get a higher capacity cover like a Mag Hytec.