I know this has been talked about before. But when do you guys like to change your rear diff oil? I dont see it in my owners manuel. I have a standard diff, not the limited slip. Joe

 

Usually around a 100k. I changed mine at 60k, but I use mine to tow mostly.

 

According to my owners manual, maintenance guide, and I quote:
"Rear axles containing synthetic lubricant and light duty trucks equipped with Ford-design axles are lubricated for life. These lubricants are not to be checked or changed unless a leak is suspected or if axle assembly has been submerged in water.. Non-synthetic rear axle lubricants should be replaced every 3,000 miles.."
If you don't have a copy, go to:
https://www.fleet.ford.com/maintenan...ls/default.asp

 

I wouldn't follow what the owner's manual says in this case, I change mine every 40-50k or so.

 

I first changed mine around 140k and am coming due again in a couple of thousand miles. For sure I will change again before 300k. It is about 10th or 12th place down on the "PSD List"

Synthetic gear oil is amazing stuff...