I have a 3.73 limited slip rear end on my 07 5.4 3v, tow package. I tow several times a year, about 5000 lbs. I know the factory fill is a synthetic differential fluid, however when should I be concerned about changing it out? Manual says lubed for life, I find that hard to believe, I'm at 36,000 miles?....

 

I tow occationaly and do a fair bit of mild off roading. I changed mine out at about 60,000 miles. It wasn't "bad" but the diffs deffinitely were well on thier way to needing a change. Better safe than sorry but I wouldn't worry much about it till around 60k.


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I was just looking into this yesterday for mine and the first call for changing the rear, front, or transfer case fluids I found was at 150k I think.

I'm like you though... kind of thinking that's a bit much.

Guess as long as your not severe service or get in deep water, you might be ok?