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  1. #1

    Default Crazy Electrical Coolant Temperature Reading

    I have Googled and searched for an answer and I am left with two options. The problem is when I bought this 86 GT the temp gauge did not read anything. I did the usual tests pulling the wire off the sender and grounding it out and watching the gauge swing one way then the other. I replaced the sender and used teflon tape the first time. Dumb move. The gauge was reading but it was up under the L in NORMAL and even higher. After I read that I cleaned the tape off and it still does the same thing. I used my infrared temp gun and all around the water neck, intake and radiator it's reading around 180*. Certainly not off the charts. I tested the senders resistance with a meter and probed the top and bottom of the sender as well as the top and the motor and they both gave me about the same readings. I also probed the top of the meter to the ground side of the battery and that gave me a totally different reading. All my other gauges read correctly except for the volt gauge and they never work I see. Do I have a bad engine to chassis ground, need some sort of resistor in my gauge cluster or try another sender?

  2. #2
    FEP Supporter Broncojunkie's Avatar
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    Easy to test if your engine ground is bad. Just take a set of jumper cables and create a temporary ground from the engine to battery ground and see if your readings change.

  3. #3

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    I know there's a small voltage regulator that's attached to the flex circuit behind the gauge cluster. I'm not sure how to test for that, but here's what you could try; If you get to the flex circuit, you could try to clean the connections at the gauge itself. Maybe it's just a bit corroded?

  4. #4

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    When that goes out usually
    A) the gauges absolutely peg

    or

    B) none of them read anything at all

    unusual to see only one doing that. It points to a different problem. Like an air pocket or low coolant, etc. Or timing too far advanced.

  5. #5

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    Quote Originally Posted by erratic50 View Post
    When that goes out usually
    A) the gauges absolutely peg

    or

    B) none of them read anything at all

    unusual to see only one doing that. It points to a different problem. Like an air pocket or low coolant, etc. Or timing too far advanced.
    The goofy thing is that it most likely isn't really hot based on the temp gun.

  6. #6
    FEP Member
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    Sounds like the wrong sensor. They come in different ranges.

  7. #7

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    I might end up trying another one once I exhaust the other trouble shooting ideas and again verifying coolant temp with my gun.

  8. #8
    FEP Senior Member dagenham's Avatar
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    My 85 reads exactly the same. I replaced the sender in the intake with an Autozone part first. I thought it was just junk so I just replaced the sending unit with a Motorcraft part and the gauge reading did not change. I suspect a bad gauge and I am going to hookup a mechanical gauge in the same hole to see what it reads and go from there.

  9. #9

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    I got mine at Pep Boys. I attempted to hook up a mechanical gauge that a buddy let me borrow but for some reason it didn't work. I put a little torch to the tip of it and still nothing so it was DOA when he gave it to me. I was thinking of ordering on from LMR that is a known part but haven't gotten around to it. Let me know what you find out. From what I read if it was just the gauge then the other ones in the dash would read funky too since it's electrical and uses resistance to get it's readings like the fuel gauge.

  10. #10

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    About 10 years ago, I chased down over heat gremlins. I changed rad, water pump, fan clutch, ‘stat. I would still experience scary temperature fluctuations. I changed the ‘stat to a “Prestone premium ‘stat”. I had tried a ford motorcraft and then a mr. Gasket ‘stat. Car would then never go above the R in NORMAL. Would still fluctuate between th N and R. Could never figure out way. Could be in traffic, AC on, or driving it hard. I could never understand the fluctuations.

    Then I was driving home from my annual hot rod weekend I host at the cottage. I was doing 70 mph and I see temps creeping up. Saw the oil pressure go up too. So I bang on the gauge cluster area where the ivr is located. Guess what?

    Temps dropped, oil pressure dropped too.

    So I replaced the ivr with a new solid state ivr. No more temp fluctuations! Oil pressure was really low. I replaced the oil pressure sending unit with a mcparts store (back in late 80’s I went through 3 ford oil pressure senders, mcparts worked for years) sender.

    I had a a stock ivr but decided to go with the solid state one. All my gauges now work properly.

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