Anyone using 75w140 weight diff fluid for their 2015+ F150s? I'm getting ready to do my transfer case, trans fluid, front and rear diff fluids and wondering if I should go with the higher weight fluid for the rear diff for longevity. Anyone switch to 75W140 and have ill effects or notice any improvements?

 

Following for interest, but also wondering why you're changing the diff fluids? They don't need to be changed unless they've been submerged.

(Notice I said need. I understand just wanting to do it.)

 

I didn't do the 75 W 140 in mine but did use the 80W90 spec that was used in the previous gen when I changed mine at 70K miles. I believe the only reason they play with the weight is for fuel efficiency. Mine drives and behaves exactly the same, of course the change in weight for me was minimal.

 

248F or less peak - 75W-90
248F plus peak - 75W-140

​​​​​Those are the guidelines I was given for optimal component life in commercial applications by the major lubricant suppliers.

Intervals are 500,000 - 750,000 mi depending on component supplier.

 

My 2005 Hemi Durango uses synthetic 75W-140 as factory fill and requires changing every 15k. I always wondered what they're hiding.

 

Well I went ahead and did the front diff with 75W90 Mobil 1 and the rear diff with 75W140 Mobil 1. The front will likely keep that weight fluid until the cover comes off as that was a PITA to vacuum out. I went for a 20 minute drive around town and didn't notice much of a change. Going on a highway drive tomorrow so I'll see if I notice any reduction in the clunk I occasionally feel when accelerating after coasting. I'd like to replace the rear diff cover with one that has a drain plug so I can replenish it with fresh fluid every so often. May go back to 75W85 for the rear when I change the diff cover just to stay within spec for warranty.

I decided to change the fluids because the truck is new to me and while 33k miles is low to be changing these fluids, I wanted peace of mine as I don't know how the truck was used prior to me owning it.

 

I can definitely understand wanting to have the peace of mind on a new-to-you vehicle.
I just always assume the OEMs, having spent millions of dollars to figure out these things (and thus avoid costly warranty claims) have specified the correct oil weight.

 

What does that mean? THe 248F or less and the 248F plus peak?

 

If the peak operating temperature is less than 248F then use 75W-90. If the peak operating temperature is over 248F then move up to the heavier 75W-140 lube.

 

How would I know that?