Ohhhh, I HATE to be the bearer of bad news...

Pull your spark plugs.  Are one or more of them EXTREMELY clean?  Do you seem
to be unable to get all the air out of the cooling system?  Does the cooling
system pressurize (from cold) in about two minutes?  If so, the reason that
your van is overheating is that it has "blown" a head gasket internally.  Not
as common as the "dripping coolant syndrome" but it does happen.  My '83.5 did
this for about a thousand miles before I figured it out.  A trip to just about
any reputable mechanic will confirm.  Have him/her check for exhaust gas in
the coolant.  Note: With the vanagon, there are not the huge bubbles that one
typically sees with a head gasket leak.  The mechanic has to use the blue
liquid turns yellow tester. ( I don't remember its name...)  If so, any you've
got the time/space, it's about a $200 repair.  If you have to pay someone else
to do it, figure around a grand...

Jim Arnott
WetWesties
Union, OR