Temperature gauge fluctuating

Discussion in '96+ Vortec Performance + Computer Swaps' started by White96k2500, Nov 28, 2019.

  1. White96k2500

    White96k2500 Newbie

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    okay so my temperature gauge problems started last year, when i would get in my truck to go to school when i get about 10-15 minutes from the house and I’m driving it would get to normal operating temp (around 195) it would automatically rise up to right at 280 and drop right back down to 195 then right back to 280 and drop down again then after that it will be fine the rest of the ride and i put a new thermostat in it last year and it was good until now and is doing the same thing again so from what I understand from what I’ve been readingeither the thermostat is bad again or thecoolant temperature sensor is bad any helpwill be greatly appreciated, truck is a 96k2500 with the 5.7 vortec
     
  2. east302

    east302 I'm Awesome

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    There are two coolant temperature sensors:

    1. One by the thermostat which reports to the computer and is the more important of the two sensors.
    2. One on the driver side of the block which is what the dash gauge uses.

    I would get a scanner to see what the first one is reading and if you’re actually overheating. It would probably be under Engine Coolant Temperature (ECT) sensor.

    If that value is normal, then I would suspect that your gauge issue is either due to a bad gauge sensor, an instrument cluster issue or something in the wire in between.
     
  3. White96k2500

    White96k2500 Newbie

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    where could i get a scanner at?
     
  4. 454cid

    454cid Sooper Pooper

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    In my experience when the gauge swings that much, it's been low on coolant..... normally the values are a little lower than what you're reporting, Though.
     
  5. east302

    east302 I'm Awesome

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    There are apps available that can be used with a Bluetooth OBD adapter - DashCommand and CarGauge Pro are two that I’ve used that I know read the ECT sensor. Others could probably recommend typical handheld units that would do the job.

    Or, a shop may read it for you if you ask or toss them a few bucks. It would only take a minute or two.

    As 454 mentioned, check that you aren’t low on coolant. Bleeding it probably wouldn’t hurt. Check YouTube for videos, but start the engine cold with the cap off. Add coolant as it drops (thermostat opens) and air bleeds out.
     
  6. White96k2500

    White96k2500 Newbie

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    Okay will do i was planning on flushing everything out and replacing the coolant anyway so ill do that and start from there thank yall for the replies i will let you know how it goes
     
  7. Tim W

    Tim W I'm Awesome

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    mine acts funny too. The gage will get to about 180 or 190, I think then drop to just above cold mark. I replaced my Coolant temp sender (the one on the block) and its pig tail. I flushed my whole system and replaced my radiator, and its thermostat with a 180 and bled my coolant with a spill free funnel. It made it super easy with no mess. My gauge still does the same thing. I have no clue what is wrong with it. Its like its acting normal but as soon as my T-Stat opens, the gauge drops and does not rise back up. I just monitor my temp on my Holly Sniper touch screen.
     
  8. White96k2500

    White96k2500 Newbie

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    I think if the flushing doesn’t fix it i will try to change the sensors and thermostat and if all fails i will just get some aftermarket gauges just to get it over with
     
  9. east302

    east302 I'm Awesome

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    If it’s in the cluster, I would suspect the stepper motor (and that’s not the correct term but I forget what it is) for the gauge needle. A quick swap with a junkyard cluster may confirm that. The odometer can be easily swapped over.

    Here’s a video on replacing the motors...


     
  10. 454cid

    454cid Sooper Pooper

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    Air core motor, I believe.
     
    Oldblue98 likes this.

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