I have seen the gauges go bad or out of calibration but that is very rare. A
pegged gauge and the light indicates a short somewhere. Could even be a bad
or incorrect new sensor. If the gauge goes down with the sensor disconnected
that is the problem. The gauge needle is actually moved by a heater element
on a bi-metal piece just like an early home thermostat. This is done to
provide the slow-damped movement. Reduced voltage is supplied to it and the
sensor completes the circuit to the chassis. As the sensor heats up, the
resistance decreases. Less resistance = more current = heater hotter and
gauge needle moves. Nothing complicated here. The gauge itself can be opened
and there is an adjustment within. 

Dennis 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Anthony Egeln
Sent: Tuesday, November 30, 2010 5:36 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Coolant Temp Sensor Problem

My rebuilt wasserboxer is in, and according to the installer, is running
like a sewing machine.
He was concerned about the coolant temperature gauge not moving at all, even
with the engine at temp, so he ordered a new sensor. �After he installed the
new sensor the gauge on the dash pegged on the high end and the red light is
blinking. �He replaced the thermostat and used the thermal gun to check the
temps and all the numbers check out just fine, despite what the gauge is
indicating.
The installer thinks we should install a different instrument cluster.
So I have two questions:
Anyone have any other ideas on what is causing the gauge to peg out?
Does anyone have a working instrument cluster they would like to sell?
I will add that with the old engine in, the gauge hardly even budged off the
cold line, but the red light did come in when overheated (twice when hoses
blew). �Which leads me to believe that it is the gauge that is bad.
Thanks, Anthony'89 Syncro GL (Hidalgo)