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  1. #1

    Default Temp gauge not working properly

    Hello four eyed family, getting ready to do a safety on my 80 fox and noticed that my temp gauge doesnít read properly. When it gets warm the gauge only goes up to the C and no more.

    I grounded the sender wire and the gauge does the same thing only up to the C. I also noticed that it takes a long time to get there is that normal?

    Anyways to the main question. Which is bad my sender, sensor, or guage. Anything helps!


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  2. #2
    FEP Power Member
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    Usually the IVR and not the gauge.
    Fox Body/3rd Gen MCA Gold Card Judge
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    88 Mclaren Mustang Vert 20K miles, 89 Mustang LX Sport Vert, 92 GT Vert.
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  3. #3

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    Quote Originally Posted by KevinK View Post
    Usually the IVR and not the gauge.
    +1 -- voltage regulator on the back of the gauge cluster is a possible culprit.

  4. #4

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    What are the oil pressure and fuel gauges doing? If all three gauges are affected than yes the Instrument Voltage Regulator is the probable cause. It feeds a 5 volt DC to those three gauges. If only the temp gauge is acting up and its behavior doesn't change when you ground the wire at the sender then I'd look at the circuit from that point back to the gauge. If that checks out then I'd suspect the gauge itself.

  5. #5

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    Quote Originally Posted by JacksAO View Post
    What are the oil pressure and fuel gauges doing? If all three gauges are affected than yes the Instrument Voltage Regulator is the probable cause. It feeds a 5 volt DC to those three gauges. If only the temp gauge is acting up and its behavior doesn't change when you ground the wire at the sender then I'd look at the circuit from that point back to the gauge. If that checks out then I'd suspect the gauge itself.
    The oil and fuel gauges are working good. Just did a 88 V8 swap on the old girl so had to change the fuel guage because of the ohms range but still works. Iíll have to check that circuit you had mentioned.


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  6. #6
    FEP Super Member gr79's Avatar
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    Best way to double check real temp is add a wide sweep mechanical temp gauge with numbers.
    Or aftermarket electrical temp gauge. Have narrower sweep, less number graduations but ok.
    Permanent or temporary install.
    Both should have a separate sensor.

    Being hot out recently, mine stays solid C or a tick higher too. Mech 5 blade fan.
    Have 2.3 in car and truck. Both run almost the same. Truck will move more. Has clutch fan.
    Have mech. gauge installed in truck. 'C' is about 195. Mid on factory gauge is over 200 on the mech.
    Then all move low or high then back to normal. That is normal IVR operation.
    IVR affects all gauges. Fuel, temp, oil press will go slightly high, low, or normal at once.

    Usually reads on the C in summer, low end of NORMAL in winter.
    May go higher then normal but cannot monitor when driving. Happens within a minute.
    Say mid R then drop in few seconds.

    My LTD LX 5.0 HO used to run in the middle straight up 'R' or higher.

  7. #7
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    The fuel gauge does not usually concern people since it rarely stays on full. It’s usually some place in the middle. The fuel gauge usually stays on the top half range longer than the bottom half. Plus once you get down to 1/4 you start thinking about filling up.

    The oil pressure might concern some people but for the most part, the middle is good. A little high or a little low, no one worries much as long as the engine is not making any noise.

    The temp gauge is the one we all watch. It’s starts out low and hopefully settles in the middle.

    Each gauge is scrutinized differently.

    A bad IVR will often show up when the alternator puts out more power/voltage. So if it’s at night with the lights on, heater or ac on and the temp goes up, it’s a bad IVR. It took me a while to realize every time the seat heaters were on, the temp gauge read hot. The thermostat and fan clutch can affect things as well.
    Fox Body/3rd Gen MCA Gold Card Judge
    84 SVO 24K miles, 85 Mclaren Capri Vert. 84 GT Turbo Vert.
    88 Mclaren Mustang Vert 20K miles, 89 Mustang LX Sport Vert, 92 GT Vert.
    03 Mach 1 7900 miles, 69 Mustang, 67 Mustang, 14 Mustang CS/GT,
    15 F150 FTX Tuscany, 16 F250 Crewcab, 67 Tbird 47K miles

  8. #8

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    Update on temp gauge. I had a spare cluster and stole the IVR off of it. Guess that wasnít the problem because the gauge is still sitting at C.

    I noticed on the back of the cluster there was a black wire with green stripes not hooked up. Is that for the temp gauge?

    I also swapped the gauge from the spare cluster and ordered a sender.

    I had put a test light on the sender wire and noticed that the current was pulsing is that normal? Thanks for all the help already guys!


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  9. #9
    FEP Super Member gr79's Avatar
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    Black wire with green stripes. Does it have a boot on the end?
    Does car have Graphic Display?
    Is low fuel light always on?
    There is a wire back there that grounds the low fuel module.
    Comes off every time cluster is removed. No fun to get back on.
    Is on the left side. Pushes onto the temp gauge ground stud.
    If left off, the low fuel LED stays lit.
    Last edited by gr79; 07-07-2018 at 02:00 AM.

  10. #10

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    Quote Originally Posted by gr79 View Post
    Black wire with green stripes. Does it have a boot on the end?
    Does car have Graphic Display?
    Is low fuel light always on?
    There is a wire back there that grounds the low fuel module.
    Comes off every time cluster is removed. No fun to get back on.
    Is on the left side. Pushes onto the temp gauge ground stud.
    If left off, the low fuel LED stays lit.
    Yes the wire has a boot. No the cluster does not have graphic display and my fuel gauge isnít hooked up because Its hooked it up to an auto meter gauge because of the different fuel tank. Would that be causing me problems if not everything is hooked up?


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  11. #11

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    Issue Resolved! I picked up a sender because I was all out of options and whala the guage works. I am still confused on why the gauge didnít max out when it was grounded but anyhow it works! I ainít gonna complain. Thanks for all the useful info guys.


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  12. #12
    FEP Super Member gr79's Avatar
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    Great to hear.
    Thanks for reporting the solution.
    Lots of times we wonder if fixed or not.
    Every bit of successful diag and repair helps others.
    From what i read too, wire off-zero, wire grounded-max scale.
    So they say...

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