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RHEOSTAT

2K views 13 replies 6 participants last post by  55 Tony 
#1 ·
first, i think that`s how it`s spelled ok, just talked to an old timer at a fall[so they say], who had a "SUN BLUE-LINE" temp gauge for sale. so, i ask him, if he had a sending unit for the gauge. he said, why not use a rheostat? so, he told me his is in his car for more that 10 years, no problem. set it up with a mechanical gauge in the top of the radiator, to 190 degrees. which he said is true, who cares about the lower temp. so he adjusted it to be the same temp at 190.ok, so, is this guy bull///ting me or what? what do ya think?
 
#2 ·
sounds like BS to me. you have to have a sending unit that is in the ball park close for that to half assed work.
 
#4 ·
Anytime you put a resistor, variable or fixed, in series with a sender, you introduce a non-linearity into the temperature vs. resistance curve.

Bottom line is you can make it read "right" at one temperature but not at a temperature above or below that temperature. The error can be quite large at other temperatures.

Best thing is a correct sender.
 
#7 ·
Now wait a minute, I read this again. I thought he had some type of electrical sending unit for a cap in the radiator and was using a rheostat to adjust that. But you say the cap stat is mechanical (or whatever kind of gauge it is he used on top of the radiator?).

If this is the whole story, then yes he set the gauge to the temp it was once 10 years ago and now it always reads that temperature. It would go to that temperature as soon as the ignition is turned on. Unless there is something else we are missing from the story?
 
#11 ·
OK, he MUST have a sending unit of some sort. He had to. There is no way in heII it could have worked without one. No way. He simply never had the *correct* one for it. Now if you knew what sending unit he was using and what resistance the rheostat was set at, then you could duplicate how it worked. Just get a resistor close to that value and either put it in series with the sending unit wire or parallel from the wire to ground. That could be done at the gauge end. If you know what kind of vehicle it was in ask him if that is what sending unit he added the resistor to.... if it had it's stock sending unit.
 
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