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Temp sending unit question

552 views 2 replies 2 participants last post by  GilaMtnJeep 
#1 ·
I have an 84 CJ7 with the original 258 6 cyl. For long time have had issue where temp guage goes up slowly to about normal, then quickly pegs itself. How can I pinpoint if it is the sending unit, or the guage, or a short in between? Please keep responses simple, as I am not a mechanic and have no understanding of electrical.
Thanks!!
 
#2 ·
Clarification

It has run normally for long time with guage issue. I have checked temp with laser type thermometer. Coolant is flowing well. I am just now re-doing the cooling system- new radiator, thermostat, heater hoses. Water pump is relatively new and working well, other hoses are newer and still good. Just can't figure out why guage says it is overheating when it isn't.
Thanks again.
 
#3 ·
The sending unit is a type of resistor. The hotter it gets, the lower the resistance. If you ground the wire to the gauge it will climb to it's maximum reading. Hook one lead of an ohmmeter to the terminal on the sensor and the other to the block and run it until it's warm. You should see a gradual drop in resistance. If the resistance suddenly drops off the sending unit could be the culprit.
 
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