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Temp Guage not working!

Discussion in '40- & 55-Series Tech' started by RyRy, Dec 25, 2003.

  1. RyRy

    RyRy

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    My Temperature guage doesnt work at all... How do these things work? All i know is that if i take a wire from the positive terminal on my battery and touch it on the wire coming from the thermostat, the guage rises right up to the maximum. I guess this tells me the guage is okay...
    What else could it be? Any help would be greatly appreciated

    Ryan
     
  2. bj42turbo

    bj42turbo

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    RyRy
    My opinion with electrical things is, unless it is a really obvious fault, I would take it to an auto elec.........Dazz
     
  3. IDave

    IDave

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    Did you look at the other end: that is, is it plugged into your temp sensor on the engine? Mine is easily disconnected when I am fiddling around with the valve cover. Also, the temp sensor may be bad: probably is from what you are saying.
     
  4. hammerhead

    hammerhead

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    If the guage and wiring test out properly then it must be the sending unit.
     
  5. RyRy

    RyRy

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    How would i tell if the thermostat is working? The wire is definetly plugged in.
     
  6. Frederik

    Frederik

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    first of all, clean the electrical contacts of the sensor and the plug. Mine were rusted but with a little sand-paper and some contact-spray, I got it to work again. The temp.sensor is a NTC (negative temp. coƫfficient) so, the higher te temperature, the lower the resistance and the higher the current to flow to the gauge.

    As you said, you bypassed the sensor, so the flaw is not in your gauge.
     
  7. arutgers

    arutgers

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  8. IDave

    IDave

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    RyRy, I think you've figured it out. Unless, as Frederik says, the contacts are substantially corroded, your sensor is the problem.
    You'll probably want to replace it. Make SURE you get the correct one, since it is possible to have the wrong one fit in there. I know this, because that is what my PO put in my rig, so the guage ran backwards!
     
  9. Klunky Chris

    Klunky Chris

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    I'll ask this here because I'm also having a temp sensor issue. The gauge doesn't move past the bottom cold mark.
    I thought the sensor was bad because after driving the 77 FJ40 for 20-30 minutes the sensor was at a very high 100 ohms.

    I replaced the temp sensor with a new Toyota and it still
    doesn't move past the very bottom of the gauge!!
    I drove the cruiser around for 20-30 minutes and the radiator seemed hot to
    the touch, but the sender was still showing 100 ohms?!? This is exactly what
    the old sender was showing. (maybe it wasn't bad?)

    90 ohms = 60C/140F
    50 ohms = 80C/176F
    27 ohms = 100C/212F
    23 ohms = 105C/221F

    Gauge seems OK as I double checked it by shorting it to ground through a 5
    watt bulb and it flashes correctly and the gauge moves to hot OK.

    could I have a bad thermostat / gasket that is not letting the engine heat
    up? The heater seems weak, my 74 heater will almost burn you, but this one
    is *warm*
    I thought maybe it was clogged, but now I'm wondering if the 100 ohms is
    correct because the engine never warms up? That would mean it's at a
    constant 100-120F??? seems low, but maybe possible?

    Anyone have any ideas?
     
  10. Ming89FJ62

    Ming89FJ62 I smell bacon GOLD Star SILVER Star

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    Klunky,

    Same problem w/ my 55. Ended up that the PO had not installed the second gasket on top of the thermostate which let enough water/anti-freeze past to make it run "cold". This would also explain your not so hot heater. I also replaced the POS with a Toyo thermostat and new gaskets - problem solved. Also, make sure that you don't have air trapped in the cooling system - you may need to "burp" your cooling system. Figured this out after I replaced the temp sensor and got no improvement.

    Ming
     
  11. Klunky Chris

    Klunky Chris

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    so....
    looking at the new Toyo thermo and gaskets (2 of them)...
    It looks like the *base* gasket just sits on top of the thermostat?!?
    do I need FPIG or anything like that or just screw it down???
    http://jeffzepp.cruiserpages.com/tech/staywarm.htm

    trying to make sure I do this right.....

    done it before, but not *sure* its right ::)
     
  12. IDave

    IDave

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    There's a little ring on the thermostat that holds the gasket, and the housing holds it on the other side, IIRC. Just screw it down.