This summer the temp gauge on my 86 Westy started runing at about 3/4 or
higher during normal driving.  To make a long story short i replaced the
t-stat, radiator, temp gauge sender, temp gauge voltage regulator, h20
pump, coolant tank cap, and flushed and bled the system many times before
giving up and taking it to a mechanic.  It was determined by using an
infrared thermometer that the van was not overheating.  For some reason
the gauge was (and still is) operating incorrectly.  While at the shop I
aquired the following resistance values for the 2.1 L temp gauge sender:

32 F    5,000-6,500 Ohms
68 F    2,000-3,000 Ohms
104F    1,000-1,500 Ohms
140F    500-675 Ohms
176F    275-375 Ohms
212F    150-250 Ohms

The above info is from AllData Corp and is not available in bentley but
should be so you may want to save this.
My temp gauge still reads high and i don't know why but I watch it for
changes like if if the needle hits the upper line and the fan starts
running then I will know its overheating.

Another note: I heard that radio shack is selling infrared thermometers
for around $50.  Not sure if these are suitable for our application but
worth looking into anyhow.

Hope this helps someone,

Andrew Fox
Ft. Collins CO
http://www2.hawaii.edu/~andrewf/vanagon/links.htm