Can a coolant temp gauge go bad?
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Thread: Can a coolant temp gauge go bad?

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    coaltrain's Avatar
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    Can a coolant temp gauge go bad?

    Need some help diagnosing an issue - my aftermarket coolant temp gauge on my 2520 quit working. I had to install one since Deere decided to not include one on this tractor - shame on them!

    This is the gauge I bought and installed in 2015 - it has worked perfectly until a couple days ago.

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    Click image for larger version.†

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    2 days ago the gauge was becoming erratic. It would be showing the proper temp then the needle would get erratic between that temp and zero (all the way low), then be OK for a minute and back and forth. As of yesterday the needle wonít move. It acted as if there was a short in the power or ground wire.

    Pulled the dash cowl off this morning. Visually checked all the wires and found no breaks. Tested for power and ground at the gauge and were fine. Did a continuity test of the lead that goes to the sensor and that is fine.

    So wondering what to try next or just order a new gauge with sending unit. I donít know if gauges like this can go bad or if the sending unit can go bad.
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    spferdil's Avatar
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    Either one could be bad, my first guess would be the sensor. The sensor is just a thermistor, meaning a resistor that changes its resistance value with temperature. And the guage is just a volt meter calibrated to read the resistance change in the sensor. Several Youtube videos on checking sensors on cars but principle is the same for all, connect an ohm meter to the sensor and see if the resistance changes while applying heat - resistance should go down with heat.
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    Like all things electric/electronic, things will go bad. This reminds me about my Jetta TDI, temp gauge started doing the same thing, reading started varying while I was driving. Temp moved up and down about 30 degrees while driving steadily on the highway. Since it was still under certified warranty, I let the dealer fix it, could have been the wiring, the dash cluster, the thermostat, or anything in between. It just turned out to the the sending unit. Gauge has been good since. I did replace the thermostat years later, but that was because it was opening too soon.

    In your case, I would just buy another, replace one piece at at time (if it is the exact same thing), or just replace the entire setup and be done with it. Your link showed it's just about $33. For me, the time spent trying to diagnose, finding a place to buy a sender or gauge separately would be more trouble than spending that $33.

    Just my 2 cents. Good luck with this.
    Tom

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    My guess would be the thermistor in the sending unit.
    Did you do a continuity check of the sending unit and what ohm reading, if any, was it?

    You can also do a continuity check across the meter posts, you should also get an ohm reading, unless it's open.
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    Quote Originally Posted by coaltrain View Post
    Need some help diagnosing an issue - my aftermarket coolant temp gauge on my 2520 quit working. I had to install one since Deere decided to not include one on this tractor - shame on them!

    This is the gauge I bought and installed in 2015 - it has worked perfectly until a couple days ago.

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    Click image for larger version.†

Name:	6D03A952-7373-4DC3-AD4B-D68057B6A0FA.jpeg†
Views:	6†
Size:	93.6 KB†
ID:	620266


    2 days ago the gauge was becoming erratic. It would be showing the proper temp then the needle would get erratic between that temp and zero (all the way low), then be OK for a minute and back and forth. As of yesterday the needle wonít move. It acted as if there was a short in the power or ground wire.

    Pulled the dash cowl off this morning. Visually checked all the wires and found no breaks. Tested for power and ground at the gauge and were fine. Did a continuity test of the lead that goes to the sensor and that is fine.

    So wondering what to try next or just order a new gauge with sending unit. I donít know if gauges like this can go bad or if the sending unit can go bad.
    Itís a simple voltmeter calibrated against temperature. It could be a number of things. You might luck out and itís an intermittent connection on the wires. You could also take a dc variable power supply and apply a test voltage to move the meter and check its function. After that, you can Check whats driving it and what itís connected to.
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    coaltrain's Avatar
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    Thanks everyone. I didnít take an ohm reading of the sensor - didnít know what I was looking for until now. Itís easy enough to check so I will just for fun.

    Iím going to order a new gauge - the sensor comes with it. Wonít hurt to replace the sensor if needed and have a spare gauge.
    Tomfive and PJR832 like this.
    ~Stan~
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    I would just replace all as you stated you are doing due to the critical data that engine temperature represents.
    I would also think that the gage may be tested in a fashion using 1.5 and 9 volt batteries, just for experimental diagnostics.
    Either way an intermittent fault will be extra trouble to reproduce.
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    As youíve seen from the responses above-as with any man made mechanical device it can fail.
    BigJim55 and coaltrain like this.
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