It is possible for the radiator to suddenly fail. The internal parts can
crack allowing coolant to enter and return without actually traveling
through the radiator. 
Get the proper thermostat and replace that first. They do wear and can fail
and should be replaced after any overheating or coolant loss event. They
work by expanding wax and if the wax is overheated or leaks out the stat
will lose function. 

It is also possible the cooling system is fine and something happened to the
gauge. 

Dennis 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Jim Felder
Sent: Saturday, March 05, 2011 2:39 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Overheating problem 91 2.1

The reason that I'm not focusing on the radiator at this time is that this
happened suddenly. It never overheated until around Christmas, and suddenly
I have a spate of little overheating issues. Filling with sludge is the kind
of thing that usually happens slowly. I know there are exceptions but it
seemed to come on pretty fast for something that normally takes place over
time.

My wife ad an acura once where the metal pin that goes into the frame above
the bellows broke. It would run differently depending on how the pin was
cocked, which would cause it to either take forever to heat up or to
instantly overheat randomly with each heating/cooling cycles.
And sometimes it ran normally. What a booger to locate and fix.

Glad I'm working on a vanagon this time... except for pulling the rear seat
to get to that split heater valve. I hate that job on a vanagon, I would
rather pull the dash.

Jim

On Sat, Mar 5, 2011 at 1:19 PM, Loren Busch <starwagen@gmail.com> wrote:
> �RE: Overheating Problems
> I'll second the comments on the radiator. �I fought the same problem 
> for several years in my '85 1.9L and it finally turned out to be the
radiator.
>