Coolant sensor

Discussion in 'Inboards' started by mikealston2428, Oct 31, 2016.

  1. mikealston2428
    Joined: Jul 2011
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    mikealston2428 Senior Member

    Hi all
    Been getting incorrect temperature readings at gauge on my Chevrolet 350 inboard
    These pictures show the stamped numbers on the sensor
    Because a new sensor is cheap I'm going to replace it
    It's an inline unit in the coolant line
    I can't seem to find any new one with these numbers
    Any help would be greatly appreciate
    Thanks
    Mike
     

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  2. mikealston2428
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    mikealston2428 Senior Member

    Any picture

    One more picture
     

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  3. PAR
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    PAR Yacht Designer/Builder

    You want the; Mercruiser 806490T, OMC/Volvo Penta 3853787, Sierra 18-5897, Mallory 9-42400, all of which are 3/8" x 18 thread, which is what it appears you need. About $15 bucks.
     
  4. CDK
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    CDK retired engineer

    Mike, if it is marked "96C =/-3C" the object you pictured is not a sensor but a thermal switch. It can be connected to a warning light, buzzer or a fan relay but not to a gauge!
     
  5. mikealston2428
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    mikealston2428 Senior Member

    Hi guy's
    Ok sounds like the auto electrical guys I had wire the engine up when I put the engine back in the boat have wired this up incorrectly
    The sensor if put pictures up of is inline in the coolant line and hooked up to the temperature Guage on the dash board
    There is a light on the dash should I hook this up the that ?
    I've ordered a sensor as per Pars reply
    Does this one goes in the block somewhere and to the dash temperature gauge ?

    Thank you
    Mike
     
  6. mikealston2428
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    mikealston2428 Senior Member

    Looks like dash gauge wire hooks up to this

    Light on dash has no wiring
    How do I wire this up to coolant sensor
    Am I correct in thinking the light comes on if the coolant gets to hot?
    With the 96 stamped on the sensor at what temperature will the light come on ?
    Thanks
    Mike
     

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  7. PAR
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    PAR Yacht Designer/Builder

    There are three places on this engine you can place a temperature sensor. You can even get a thermostat housing that has a boss for a sensor. On your engine the common locations are on the side of the heads, either between #1 & #3 or #6 & #8 cylinders and on the intake usually right near the thermostat or on the crossover passage. The head locations are more accurate and can show temperature rise under load, while the intake will "average" the temperature, by the time the coolant get there. If you're real anal about things, run a gauge on both head boss locations. The head sensor location will appear to run hotter, than the intake location, especially after shutdown. Most of the factories are using the intake location, for lower and more averaged readings.

    There's a difference between a temperature gauge "sender" and a temperature switch. A sender just offers the temperature for the gauge to display. A switch will be preset to close a circuit at a specific temperature or temperature range. These switches are handy for idiot lights, turning on cooling fans, overheating warning buzzers, etc. Decide what temperature you want to be notified about, when a buzzer, light (or both) go on and install it in a "T" fitting where the temperature sender is, or any other of the usual coolant sensor locations (there's quite a few if you own a tap and die set). I like the "T" fitting idea, as the temperature is consistent between the sender and the temperature switch, which isn't the case if one is on the head and the other on the intake.

    On SBC's I do, I like to use the Chevy truck thermostat housing, which has a sensor boss right on top of it. I thread in "T" fitting and can place a gauge sender and a switch.

    [​IMG]

    This is a truck of course, but it shows the thermostate housing I'm talking about and next to it (circled) is a temperature switch location, which is in the crossover passage on the intake. Most intakes have a few different locations, where there's a plug or boss that can be removed or drilled and tapped for a sensor. Again, for consistency, pick locations that are near each other.
     
  8. mikealston2428
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    mikealston2428 Senior Member

    Thank you Par very much appreciated
    Its all clear to me know
     
  9. CatrigCat
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    CatrigCat Junior Member

    Great info.
    To clarify, the temperature switches above are only for overheat warning lights.
    The cooling fan temperature switch is either on the bottom of the radiator or the thermostat housing if located on the lower/return hose.

    Some cars had two temperature sending units, one for the dash gauge and one for the ecu.
    If there was an extra warning light, there was a third sensor.
    Then, on later models, there was only one sensor and the ecu controlled everything, both the gauge and warnings (the cooling fan still requires a seperate sensor).
     

  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    There are several reasons you might want a temperature switch, besides warning lights. In modern automotive applications there are several temperature sensors and switches.
     
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