Originally Posted by whippersnapper02
Everything is in your owners manual. 80W-90. If you have a L/S then you need a bottle of friction modifier from Ford.
To check if you have a L/S or not look at the chart:
Glad I found this thread, so since I have an L/S can you get the friction modifier stuff somewhere other than thedealership? I need to change my pinion seal. the truck didn't come with the owners manual when I bought it (weird I know) so 80w is good or should I get something thicker or whatever.