Temperature Sender & Instrument Gauge Problems

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    Author Topic: Temperature Sender & Instrument Gauge Problems  (Read 4494 times)

    Offline NorthWestcuda

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    Temperature Sender & Instrument Gauge Problems
    « on: April 17, 2011 - 11:47:12 PM »
    I know this is “Old Hat” to a lot of you, but I can’t get my temperature gauge to register any reading (movement).  I’ve read through a lot of postings and this is what I’ve done so far.  Oh, I have a 73 cuda with a 440.  These are the things I tried with the key on:
       1. I’ve grounded out the temperature wire (without sender) and the temperature gauge pegs out at “H”.
        2). I’ve made sure the threads on the drive side of the water pump, were the temperature sending unit screws into, actual will ground the sending unit.
       3). I’ve measured the resistance of the sending unit when in boiling water.  Resistance goes down to something like 60ohms in hot water. At cold it’s much higher like 120\130s.  I’m going off memory, so I could be kind of wrong with these numbers.
       4). I even tried connecting the sending wire to the sending unit, put the sending unit in a pan of boiling water and ground the treads to the battery.  Nothing happened to the gauge.

    What should I do next guys?  Thanks
    « Last Edit: April 18, 2011 - 01:10:37 AM by NorthWestcuda »
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    1973 Cuda, 440 engine
    1972 Chevy 4x4 PU stepside
    2003 Ford F-350 Diesel


    Offline Bullitt-

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    Re: Temperature Sender & Instrument Gauge Problems
    « Reply #1 on: April 18, 2011 - 08:30:45 AM »
    Based on these #s  the sending unit may be bad


    http://www.cuda-challenger.com/cc/index.php?topic=39320.msg393041#msg393041

    Quote from: 67Vette427 on November 16, 2007 - 08:24:44 PM
    I measured the new one I got from pepboys and it came out pretty close as the Napa.

    Napa

    cold 71* 255 ohms                 warm 180*    33 ohms

    Pepboys

    cold 71* 200 ohms                 warm 180*     31 ohms
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    Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
    Screwed by Photobucket!

    Offline UKcuda

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    Re: Temperature Sender & Instrument Gauge Problems
    « Reply #2 on: April 18, 2011 - 06:18:25 PM »
    Yeah, what Bullitt said. 

    They should drop to pretty low resistance when hot.  It's all a bit hit and miss but 60 ohms seems way too high, and also a lot of multi-meters are not that accurate at measuring low ohms so you might even be off on that.
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    '72 'cuda

    Offline 422STROKER

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    Re: Temperature Sender & Instrument Gauge Problems
    « Reply #3 on: April 18, 2011 - 07:01:31 PM »
    Are the other gauges working?  There is a voltage limiter on the back of the cluster that reduces the voltage to 5v IIRC.

    Tom

    http://www.moparmusclemagazine.com/techarticles/interior/23241_instrument_gauges_repair/index.html
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    Tom
    12.77 @ 108.87 15" Street Drag radial tires 3.23 gear

    Offline NorthWestcuda

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    Re: Temperature Sender & Instrument Gauge Problems
    « Reply #4 on: April 20, 2011 - 12:18:30 AM »
    The gas gauge and battery charge gauge works.  I have a rally instrument panel.  I just put in a new temp sender in the engine and will start it up tomorrow and test it.  I'm also trying to reconnect my factory oil pressure gauge back up.  I installed an aftermarket mechanical oil pressure gauge when I bought the car and disconnected the factory oil sending wire.  Shouldn't I be able to ground the gray oil sending wire to the block and peg the factory oil gauge to see if it works?????  I tried that and nothing happened to the factory oil gauge.  Could I have something wrong with my factory oil gauge only?   
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    1973 Cuda, 440 engine
    1972 Chevy 4x4 PU stepside
    2003 Ford F-350 Diesel

    Offline Cuda54

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    Re: Temperature Sender & Instrument Gauge Problems
    « Reply #5 on: April 20, 2011 - 01:04:12 AM »
    Do you have aluminum heads? That can mess them up as aluminum is not a good ground.
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    Offline Cuda54

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    Re: Temperature Sender & Instrument Gauge Problems
    « Reply #6 on: April 20, 2011 - 01:07:02 AM »
    I ment intake and heads I have both on my 440.
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    Offline NorthWestcuda

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    Re: Temperature Sender & Instrument Gauge Problems
    « Reply #7 on: April 20, 2011 - 01:30:52 AM »
    Intake manifold is aluminum but the heads are "stock" metal heads for now...
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    1973 Cuda, 440 engine
    1972 Chevy 4x4 PU stepside
    2003 Ford F-350 Diesel

    Offline UKcuda

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    Re: Temperature Sender & Instrument Gauge Problems
    « Reply #8 on: April 20, 2011 - 03:44:32 AM »
    Quote from: Cuda54 on April 20, 2011 - 01:04:12 AM
    Do you have aluminum heads? That can mess them up as aluminum is not a good ground.

    Aluminum (we say aluminium) is actually a better electrical conductor than iron.
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    '72 'cuda

    Offline NorthWestcuda

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    Re: Temperature Sender & Instrument Gauge Problems
    « Reply #9 on: April 21, 2011 - 04:59:24 PM »
    OK.  More help please.  I put in the new temperature sending unit and started the car.  Nothing registered on the factory temp gauge after the engine heated up.  So I again shorted the temperature sending wire and actually sat down and watched to see what the temp gauge was doing.  It initially started to raise than fell some and again continued and pegged out completely and then fell some and continued to act like someone was pulling the ground “On and Off”.    I watched this for about one minute and than plugged the wire on to the sending unit and started the car.  The gauge than started to actually work for awhile, it would fall some and work again. Any idea what’s going on with this temp gauge?  Does it sound like something is wrong with the voltage limit regulator on the back of the instrument panel? 
    « Last Edit: April 21, 2011 - 05:41:58 PM by NorthWestcuda »
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    1973 Cuda, 440 engine
    1972 Chevy 4x4 PU stepside
    2003 Ford F-350 Diesel

    Offline UKcuda

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    Re: Temperature Sender & Instrument Gauge Problems
    « Reply #10 on: April 21, 2011 - 05:44:05 PM »
    It could be the regulator but it sounds more like the gauge is faulty.  I had one that behaved like that, it would rise normally and then snap back a little way, and then continue to rise again.

    They are fragile little things with an arrangement of a heater wire wound round a bi-metal strip, a couple of pivots and springs.  They can easily go twitchy.

    To make matters worse, as the gauges heat up their own resistance increases.  I believe that's why the oil and fuel senders are wound with the resistance wires close together at one end and wider apart at the other.  I did look into all this in some detail a while ago when I built my own regulator, but I can't remember now what the change is, I think the gauges start off at about 10 ohms and end up nearer 30 when they are hot at full deflection.

    If you can get hold of a variable DC voltage source (like a train set controller or something) you can test your gauge by turning up the voltage gradually from zero and see if the gauge responds in anything like a linear way.  By the time you get to about six volts it should be full across the scale.
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    '72 'cuda
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