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I have read all the past posts about coolant temp guages and sending units. What is the definitive test to tell if a stock 1969 console mounted coolant temp. guage is broken (vs. the sending unit)???? Mine worked last year just fine , now it doesn't vary with temperature. Grounding the sender "post" on back of guage "pegs" needle hot. Guage dos not go to cold when sender is disconnected. Going from boiling water to ice water shows little change, almost none ( how fast should it react ? ). I was going to put a variable resistor across it next to see if I can get it reponding. Thank you in advance for the help !!!
 

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Get a variable resistor of about 1K to 5K ohms. Attach the wiper (center terminal) to the sender wire. Attach one of the other two terminals to a good ground. Turning the pot should sweep the guage. I think operating resistance is in the neighborhood of 100 ohms but I'm not certain of that. In any case, you should be able to diagnose the guage.

Take a resistance reading off the sender between it's unconnected terminal and the block. When hot it should be in the 100 ohms range and cold it should be several hundred ohms to thousands. It may be the other way around, but at least you'll know if it is changing resistance with temperature.
 

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Thanks dnult !

My gauge is bad. Windings "look" fine , but magnetic field is created in one direction only. As I was lloking at the thing completely disassembled , I realized it was easy enough to put the "guts" from another (modern) temperature gauge in the housing from 1969. Looks stock except for electrical connections which are hidden , and the needle is different , not bad , just slightly different shade of orange. While fussing with it , I checked the accuracy (boiling water & thermocouple w/readout) of the gauge and set the needle so that 190 deg. F is straight up. I am most happy.
 

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Excellent John.
 
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