While I was under the truck looking for the source of an oil leak I noticed a line coming off the back of the motor, passenger side near/under the transmission dipstick. I followed it to a large canister(size of a soccer ball maybe) mounted to the frame on the driver's side, then a return line leading to back of oil cooler elbow. Is this an additional oil cooler U-haul put in or better yet a centrifuge?

 

Here's some info on a truck like that. It says they have a bigger oil capacity then normal trucks. That's what thing your talking about is.

Early 90's IDI Uhaul truck Value

 

I've seen the part on the uhaul parts website and wondered how it was plumbed in. If you could shoot some pictures and post them that would be great.