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water temp guage problem

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by chris672, Jun 12, 2002.

  1. chris672

    chris672 1/2 ton status

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    My guage was reading really low(about 100*) so I change the thermostat. It still read low so I grounded the wire from the sending unit and the guage pegged on the high side. That means the guage is ok, right? I changed the sending unit and now the temp reads 260*+. What is wrong? Wrong sensor?
     
  2. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Wrong sensor. Temp sensors work off a resistance principle. When the sender is hot, it will conduct better and offers less resistance. When you groud the wire, you take away resistance. The sender allows the wire to ground a little, but not fully, so you can get your readings.
     
  3. chris672

    chris672 1/2 ton status

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    The first sensor that they gave me was the one for the computer, found that out after I had already installed it (I told them for the guage). The second one they gave me I told them to make sure that it was for the guage and they gave me one that still didnt work so they gave me a third sensor and now when the truck is cold the guage reads 110? and then slowly goes up to 260*+.
     
  4. ZZ4x4

    ZZ4x4 1/2 ton status

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    Yup, same here. I must have tried 10 sensors trying to get the right reading. I finally put the sensors in the oven and got them to 250 degrees. I then measured the resistance across the sensors. I also put different resistors across my gauge wires to find out how much resistance the gauge liked. Ended up with a sensor which was close to pegging the gauge at 250. I then added a small resistor in series to get the gauge reading exactly where I wanted it. To note: there is a book of sensors telling the resistance ranges and part numbers at O'reilly's Auto parts (and probly most parts stores). Good luck. JT
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    I went to a wrecking yard and pulled a few. Apparently 20 year old GM parts are more reliable than 6 month old repro stuff.
     

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