I'm forwarding this to the vanagon list. Others there may
have more insights.

Other than the radiator you mention some, possible reasons for
hot running diesel:

1. Air bubbles in cooling system. Bleed carefully. Check
for air at radiator bleed nipple.

2. Substandard waterpump. There are several aftermarket ones.
The better ones have a cast metal impeller. Some very cheap ones have a pressed
steel impeller. Newer VW oem have a solid looking heavy plastic impeller.
Nowdays I don't take the risk, but use either the VW or at least the cast
impeller type.

3. Belt routing. Best routing is 2 belts: motor -> waterpump -> alternator.
Some shops put in one belt for both pump and alt. That gives very little
contact for pulleys and risk of slip.

4. Gasket between waterpump and housing. Old style is standard gasket paper.
Newer style is a thin aluminum plate with o-ring like rubber fastned
to it. Newer style gasket combined with old housing would increase the
housing to pump gap. (And thus possibly reducing flow)

5. Restrictive exhaust. Particularly noticable if you put in a more
powerful engine (e.g. 1.9l and/or turbo) and keep the original
restricitove 1.6l exhaust system.

Exactly what engine do you have now?

Good luck,
Martin

   From:        Stephen Kennedy <dr.s.kennedy@cox.net>
   Date:        Sun, 4 Dec 2005 19:20:49 -0800

   Howdy.  I have a 1982 diesel vanagon camper.  About three years ago
   the engine blew, and I had a new VW Passat diesel put in.  It's
   wonderful in many ways, although the HP isn't much greater.  But the
   big problem is overheating.  I've had the radiator reamed out, to
   little avail.  Now, before I put a lot of cash into a new radiator, I
   need to know whether these engines typically have such problems.
   Otherwise, I might sadly put it on the block.  I live in So Cal, and
   I need to be able to sit on freeways once in a while.  So my question
   is: do people with diesels typically have difficulties with overheating.

   Thanks for your insight.

   Steve Kennedy