The owner`s manual in the Explorer says " to refill the Front axle, use 4x4 gear oil" . I went to the store and a little surprise, there are two, a Sae 140 and a Sae 250. Which is adecuate ?
I have heard the Rear axle Oil is different, sae 90 i guess...
Try this website:
http://www.therangerstation.com/tech_library/index.htm
They have a large amount of information for the Exploder/Ranger.
I do know that the gearbox (Mazda 5-speed) on my truck takes ATF and NOT gear oil. I learned that the hard way.
stuff other than tractors still uses 90 wgt.. man.
Not always, many newer post 1990ish vehicals, require as thick as 140W or a 70W140 synthetic. But yes all the old RWD cars were 90W. The owners or shop manuel should specify a viscosity, they may infact recomend synthetic. Check the "fluids" section in the manuel. Or, as cougarcrager suggested, an explorer website with a FAQ or something.