92 Dodge W250 oil tank? reservoir?
 

I've got a 92 dodge W250, trying to figure out what this plastic jug/reservoir is right under and behind the passenger front tire. It has oil in it... just not sure what it's for, the turbo maybe ?? excess/blow off oil?? I have NO idea.

Jug has SAE-PE... 2PE 8255D... stamped on it.

I remember finding out what it was at one point but cant find my bookmark or I didn't save it cause I thought I'd remember what it was... :/

When I got the truck it was pretty much empty and now, a few years later it has a considerable amount of oil in it. There is a place to drain the jug, but I'd like to know what it is before I drain it out!

Help would be greatly appreciated because I've spent half the night looking in the books and online to no avail!