coolant temp sender question | FerrariChat

coolant temp sender question

Discussion in '308/328' started by AZDoug, Jul 4, 2020.

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  1. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,606
    Along the Verde , AZ
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    Doug
    As this is a variable resistor, is "hot" higher or lower resistance than "cold", thru the sender unit?

    Thanks,
    Doug
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    Hot is lower resistance.

    If you search on the "104628" part number, you'll get some prior threads that, IIRC, include information about temp versus resistance.
     
  3. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,606
    Along the Verde , AZ
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    Doug
    Thanks.
    Trying to chase down why my temp gauge sometimes reads a lot hotter than actual temp (confirmed by IR gun). It will sometimes creep up, and stay there reading around 220 and the rad fans haven't even come on,and the IR gun rad temp reads 180. I get approx the same on the t-stat housing and cross over pipe, though they read perhaps 5* less due to lower emissivity from the bare alum vs the black on the rad inlet.

    Temp will sometimes creep up,and stay there, or sometimes suddenly drop 10-20-30 degrees. Sounds like either a gauge or connection problem, but if lower resistance means hotter, it doesn't sound like a bad connection between the gauge and the sender. Same issue with two diff sendsors, so it isn't the sensor.

    Doug
     
  4. kcabpilot

    kcabpilot Formula 3

    Apr 17, 2014
    1,527
    California SF bay area
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    I had a similar problem. Only a few minutes and a couple of blocks from the house the temperature would climb up past the 195 mark but the heater was still blowing cold air. Then, just as suddenly it would drop back to about the quarter mark and then slowly rise in a normal fashion to it's regular operating temp. In my case I had a bunch of air in the system due to a leaking head gasket but you could have air for other reasons. Try doing the coolant bleed procedure.
     
  5. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,606
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    Doug
    Its not air. Its electrical. Not sure if "something", is causing an external variable ground to the gauge besides the thermistor temp sensor.

    The motor is freshly rebuilt and upgraded, and the problem existed before the recent work.

    Doug
     
  6. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,606
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    Doug
    You bring up another point to mind: I have never seen mentioned or tried to bleed the heater system. Wouldn't that be a potential air trap, also? Especially after doing a complete coolant fill?

    Doug
     
  7. kcabpilot

    kcabpilot Formula 3

    Apr 17, 2014
    1,527
    California SF bay area
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    Paul
    Just run it with the heater valves wide open and it should get circulated through. Any air in the system will eventually get trapped at the top of the radiator where you can easily bleed it out when it's cold. You just need to open the cap at the expansion tank since it's higher than the radiator.
     

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