pvc pipe??????

[NJT5047]

I'd prefer exhaust pipe bend with good quality steel over soldered copper.   As long as antifreeze is in the cooling system, exhaust pipe tubing will not rust.  It is easily bent for the application, about any size is available, cheap, and readily available anywhere.   Soldered joints on a diesel engine scare the poopy out of me.  Although, I've seen them work and last....still scare me.  Straight sections of copper pipe are great, but if you want a bend, exhaust pipe material will work better.  If you want some abstract bend, exhaust tubing is perfect.
I've used exhaust tubing for all sorts of 'hot rod' applications, some even acid dipped for chrome, with nary an issue.   I've got an Astro V8 conversion that has 9 year old steel tubing in the cooling system. NO problemo! 
One other issue, rough up the ends and use good quality clamps on smooth pipe.  Mark the hose connection so you can see if any movement occurs.   You can weld on 'retainer' bumps on both steel and copper for better hose retention.   Hoses will slide off smooth metal tubing.
While PVC isn't a cool idea, almost any steel or copper will make a workmanlike fix.  Steel and copper won't reduce the ID of the tubing either, unlike PVC. 
JR

[buswarrior]

Just to clarify, in the truck applications using steel pipe in the cooling plumbing, the pipes rust from the outside in, exposed to the road spray under the front and kicked up by the steer tires.

happy coaching!
buswarrior

[HighTechRedneck]

Just to clarify, in the truck applications using steel pipe in the cooling plumbing, the pipes rust from the outside in, exposed to the road spray under the front and kicked up by the steer tires.

happy coaching!
buswarrior

Maybe it would be useful to paint them with brake drum paint (on the outside of the pipe of course).  The paint is rated for up to 350°, doesn't require primer, doesn't have to be baked on, and comes in several colors including a nice bright silver.  For that matter, the same could be said for engine paint as well (I have just really taken a liking to the silver brake drum paint for its brightness and durability.)

[NJT5047]

How about a nice powdercoat?  After bending of course. 
JR