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I've got a '66 with a 396. When I bought the car about 3 years ago the temperature gauge (stock SS gauge with needle moving from "C" to "H") didn't work. So, I replaced the sending unit and the gauge works --- sort of. The needle is always at the hot end of the gauge. At about the 3/4 mark the engine is at 180 degrees. At the "H" mark the engine is at 197 degrees. I'm assuming that temperatures in the 180 to 220 degree range would be considered normal and the needle should be somewhere in the middle of the gauge.

I'm going to change out the temperature sending unit to see if that brings the needle down. If it doesn't, then I need to adjust the gauge. I'm thinking that if I add a resistor of the proper value in series with the sending unit, it will bring the needle down to the center of the gauge. (I can experiment with a potentiometer.) Does this sound right or am I out to lunch? Should the car run in the 180 to 220 degree range?

Thanks for your help. Greg.
 

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Greg. Generally speaking the resistance of the sender drops as temperature rises. Putting a resistor in series will help bring the needle down, but you should realize that, because the series resistor will not very with temperature as the sensor does, the indication of the needle will not be linear anymore. This effect is the most in the hot position, which is the range you will want to be to most accurate I would say. My advise would be to not use a resistor with a value greater than 10 - 15 % of the sensor's value.

Once you have determined the value of the resistor needed, you could try and find a sensor that has the sum value you want. If the gauge is at fault though, there will be no sensor that will ever work right of course.

Another route could be to open the gauge and bend the metal strip that is responsible for the needle's indication. If you are careful this can be done.

Rob
 
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