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Posted by Sherman in Idaho [72.47.9.37] on Sunday, August 26, 2012 at 12:43:54 :
In Reply to: W100 Temp Gauge problem. posted by The Dodge Boys [64.121.152.7] on Sunday, August 26, 2012 at 08:48:50 :
I hesitate to state the obvious, but maybe the temperature at the sender really is as hot as the gauge says. The first thing to do with any instrumentation problem is check the actual thing you're trying to measure, using a gauge that you know is good. In this case it could be a digital electronic thermocouple or even a mercury thermometer, put up against the head right next to the temperature sensor, and thermally coupled to it with something like a small puddle of water, some conductive putty, or what-have-you. If you can borrow one of those electronic "gun" type infrared thermometers, that's definitely the easy way to check. Just point it at the spot you want to measure and pull the trigger. I have a very cheap version that has been handy for finding heat loss from buildings and hot spots on engines and other equipment. Maybe the water passages are clogged up somehow and the sender is in a hot spot. Maybe the thermostat isn't opening all the way, and although the radiator water is only 200 deg, the head is much hotter.
Having replaced the sender and gotten the same results, I would not try to work any magic into voltage regulation. If the factory system worked originally, that should be good enough. If you really want to do the experiment, you could connect a separate fully-charged battery just to the temperature gauge circuit and see what happens. Maybe it takes 6 volts, if it's downstream of one of those primitive old vibrating-contact voltage regulators that they used for a few years on the fuel gauge circuit.
Still, my first step at this point would be to find out how hot the engine really is at the sender location. If you have a known good non-electric gauge sitting around, it might even be worth taking the electric sender out and putting the non-electric unit in just to see what it reads.
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