Date:         Wed, 12 Oct 1994 15:11:27 -0700 (PDT)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         H Steven Dolan <dworkin@netcom.com>
Subject:      Re: cyl head temp gauge

On Wed, 12 Oct 1994, David Carment wrote:

> H Steven Dolan writes:
> > 
> > Cylinder head temperature guages (and most other high temperature measuring 
> > devices) use thermocouples as sending units.  etc.......

> I apologise for my stupidity but would the additional length of wire
> running from the leads at the back to the gauge at the front need to be
> included in this calibration? This would be almost impossible to do
> accurately given the extra 8 feet of wire for each lead. DC> 

David, 

All the ones I have ever seen have a factory installed set of leads.  The
length of these leads is included in the calibration done at the factory. 
The ideal situation is not to mess with the length, as you will screw up
the calibration.  If you must, then you need a friend who works at a lab
with the tools to do the calibration. That is, if there is a calibration
screw on the temperature guage (some of the cheap ones I have seen are
sealed).  As a strictly hypothetical alternative, with no guarantee, (note
I am weaseling here) you might try this: 

1 install the sender (but leave the leads alone)
2 run the leads out of the engine compartment to a convenient place (like 
  your shop bench)
3 attach the meter to the factory length leads while it is on the bench
4 idle the car for >20 min (fully warmed up)
5 note the temperature on the guage
6 stop the car, run the leads to the dash, clip'em, splice'em, whatever.
7 attach the meter
8 run the car again til fully warm
9 adjust the needle to the previously noted temperature
10 let me know whether you shortened/lengthened the leads, and what 
   variation it caused.  (I love a good experiment)

Ideally you should recalibrate at 2 or 3 different temperature points, but
normal operating temperature is the most important.  Check your plan of
action real careful before you start cutting tho, coz' you shouldn't have
to.  I often run into situations where I spend hours doing that I could
have saved with a couple of minutes of thinking. 

					H Steven Dolan
					dworkin@netcom.com