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Temp Gauge

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Innerpiece, Sep 25, 2001.

  1. Innerpiece

    Innerpiece 1/2 ton status

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    Hey All -- Looking for wisdom, as usual

    87 K5 Silverado TBI 305 700R4 Np208 10bolt 90% stock

    I've got some wierdness going on with my temp gauge. After the truck has sat overnight and I turn the key to on, the temp gauge shows Cold (10 O'clock on the gauge). Then, without starting the motor, it gradually runs up to about 3/4 hot or so (1 o'clock) over about 30 seconds. If I then start the motor, it moves around a little erratically and jumps some and then pegs out after about 10 seconds on super hot (3 o'clock) about 1/4 about Full hot and stays there. I've put the mulitmeter on the sensor (while engine still warm) and gotten about 240 ohms resistance or so, and the sensor is getting about 5 volts to it with the key on and the motor off.

    So now the questions ...

    (1) Any thoughts?!

    (2) what is the normal resistance range of the sensor?

    (3) if the sensor circuit is open (sensor plug disconnected) (infinite resistance) will the gauge read cold or hot?

    (4) if the sensor circuit is grounded (zero resistance) will the gauge read hot or cold?

    (5) does this sound like a sensor, wiring, or gauge problem?


    Thanks for the help.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    I know the answer to none of your questions, except number one. : )

    *personally* it would seem a waste of time to try and troubleshoot that problem, although you would learn how it works, which is never a bad thing. Go to a wrecking yard, (if you even NEED an excuse to go the the 'yards!) and grab a couple of temp senders. Swap them with yours. If problems fixed, yippee, it not, repair (clean contacts, check ceramic piece on back for cracks, reinstall) or replace the gauge, and see if that works. Used senders should be free, so its not like you are throwing money at the problem.

    IIRC, the wire for the sending unit goes "straight through" from the sender to the gauge, so wiring problems are unlikely, unless the wire inulation is shot somewhere, and hitting ground intermittently. Sounds too consistent a problem for that though.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
    No anti-theft measures on your truck? No pity when its stolen
     
  3. Itali83

    Itali83 1/2 ton status

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    Just buy another sender, if a truck is in the junkyard, odds are good that most of it's sensors are junk as well. if you don't like electrical guages like me, buy some good autometers and go all mechanical. Just my .02 cents.
    Ben 87 Jimmy
    <font color=blue>Rust=Bad</font color=blue>
    <a target="_blank" href=http://www.bens87toy.alloffroad.com>www.bens87toy.alloffroad.com</a>
     
  4. Pugsley

    Pugsley 1/2 ton status

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    I'm with Ben - Just buy one. Even if it isn't the problem, chances are it needed replacement anyway. The last one I bought (last week) cost $7.99 at Napa.

    Special thanks to those lost from IAFF Locals 94 and 854 - You shall never be forgotten
    <a target="_blank" href=http://pugsley.alloffroad.com>pugsley.alloffroad.com</a>
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    I said don't pay to replace it because:

    A)throwing money at problems gets expensive when you don't know what the real cause is and

    B) I have personally NEVER seen a temp sending unit go out, nor even heard of that. (someone will say they have now though I'm sure :) Fuel and Oil yes, but NEVER a temp sender. The one on my truck now is over 20 years old, pulled from a wrecking yard, and works fine.

    And heck, grab two or three of them in the 'yard. They are on darn near every truck, and with my luck so far with 0 failure rate even on 20 year old senders, I'd not hesitate to try another used one.

    I don't have diagrams for the internals of one, but I'm betting it is a lot simpler than an oil pressure or fuel tank sending unit, so much less likely to fail. And THOSE last for 20 years too!



    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
    No anti-theft measures on your truck? No pity when its stolen
     
  6. Pugsley

    Pugsley 1/2 ton status

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    Mine died on me - it had the exact same symptoms for several days, and then just quit all together - the older ones were far better quality and materials than the newer "made in Taiwan by 8 year olds for 50 cents a week" variety. I had a 92 F150 go through 4 of Pep Boys' best in a 6 week period, before I finally got mad and bought a Motorcraft.

    Special thanks to those lost from IAFF Locals 94 and 854 - You shall never be forgotten
    <a target="_blank" href=http://pugsley.alloffroad.com>pugsley.alloffroad.com</a>
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    and you know what? Grounding the sending unit wire to the block should probably make the sending unit peg out, or go to minimum. Thats an easy check. I would suspect sending unit if the gauge responds consistently when you ground that wire.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
    No anti-theft measures on your truck? No pity when its stolen
     

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