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Thread: Temperature Gauge

  1. #1
    Senior Member
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    Temperature Gauge

    I have a roadster with '91 302 EFI motor with Speedhut gauges. The temperature gauge shows about 200 degrees steady state at cruise, but a check with a IR thermal gun at the sender shows about 180 degrees. After a brief delay (5 minutes) after shutting off, the gauge and IR temps are still about 20 degrees apart. Do I have a bad sender?

  2. #2
    Not a waxer Jeff Kleiner's Avatar
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    Feb 2011
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    Dave,
    I think the gauge is showing real data; as I said when we talked this morning I installed a 195 degree thermostat when I built the engine and car. Remember the sender probe is wet, in the coolant, so if you're shooting the IR on the outside housing of the sender unit exposed to cooler ambient air some variation is to be expected.

    Cheers,
    Jeff

  3. #3
    Seasoned Citizen NAZ's Avatar
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    IR values can be significantly affected by the materials and surface condition of the part you are taking a reading on. IR emissivity of chrome, polished alum or even very glossy paint can show a much lower value than a rough or dull surface even when the parts are at the same temp. One trick is to use a piece of painters tape on the part you want to measure if you’re getting an unrealistic reading. Also the area that the sensor sees gets bigger the farther away you hold the meter and that area can be large enough to collect reflected IR beyond what you want to measure and skew the results. And remember that an IR gun only reads surface temperature not core temp, which can be very different.

  4. #4
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    Jeff,
    After our discussion this morning, I am de-worrying.
    Thanks!
    Dave

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