I did the same thing Tod did. Guage was reading too high so I "trimmed" the
circuit and adding 4 ohms made it very accurate in the 190-200 degrees
range. If gauge is reading too low, however, this trick won't work. One
more thing to keep in mind is that the resistance curve is non-linear,
according to Stu's very excellent article. So adding resistance will only
correct a specific temperature range, most important being between
thermostat temp and boiling, of course.
-----Original Message-----
From: tigers-bounces@autox.team.net [mailto:tigers-bounces@autox.team.net]
On Behalf Of Tod Brown
Sent: Wednesday, October 20, 2010 1:45 PM
To: tigers@autox.team.net; Randy Smith; Stu Brennan; Dave Munroe
Subject: Re: [Tigers] Engine Temperature
Hi All:
As Stu has noted in his article, the gauge reading and the combined
resistance of the gauge and sender have an inverse relationship (i. e .
if the gauge reads high, it's because the resistance is too low). In my
case, when I went through the process of trying to figure out why my
temp gauge was reading high, I eliminated the voltage regulator and the
sender as the causes, first. I then measured the resistance of my gauge
and found it to be low, compared to the value of 60 ohms cited by Stu.
The cure, in my case, was to wire an additional resistor in series with
the gauge. I determined the required resistance by first inserting a
variable resistor (a "pot" or potentiometer) in series with the gauge
and adjusting it until the gauge read the rating on my thermostat once
the engine had warmed up. Then, using a meter, I measured the
resistance of the pot and took a trip to my local Radio Shack, where I
purchased a fixed resistor closest to the measured value of the pot. I
then replaced the pot with the fixed resistor and wrapped in shrink-fit
tubing. Voila! A correct reading on the gauge for about a dollar. If
you do this, make sure you use a fixed resistor that has a high enough
power (wattage) rating. A 10 watt resistor should be sufficient.
Tod
B382002384LRXFE
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