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Thread: Temperature Sensor Placement

  1. #1
    Registered Member Troy's Avatar
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    Temperature Sensor Placement

    Hello all,

    I just finished putting an engine together for my dad's '57 2 door hard top. The last engine ('67 327) had a tap on the intake for his temp sensor, the new manifold didn't have one so I put it in the head. It's always been my understanding that the head tap gives a higher temp (due to combustion) than the intake wear basically the coolant is returning at a lower temp. I noted this when dad's stock temp gauge was reading hotter than it did. Has anyone noticed this too and about how much higher would you expect. I know I'm going to have him add a shroud at some point.

  2. #2
    Registered Member WagonCrazy's Avatar
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    You will get different temps at different points around the water cooling system.
    Buy a $25 Harbor Freight laser temp gun to verify this...
    Head location for the sensor will read hottest (in general...because it is just above the cylinders where spark and combustion occur). Passenger head thermostat bung is farthest from the circulation of the radiator.
    The intake manifold, just under where the themostat sits will read 10-20 degrees cooler typically.
    When the thermostat opens, (and circulation occurs thru the radiator), all readings will drop 20+ degrees for a few minutes typically (at idle)
    Then your engine will eventually heat the water temps until your fan and radiator start to cool it.
    Doesn't sound like you have an electric fan, but if you did (or do install one), they will come on based on where you have the "low temp on" set (assuming you have some kind of settable fan controller like Dakota Digital. Spal doesnt make one anymore.)

    That's how my system works. I have one thermostat in the passenger head (direct to an aftermarket temp gauge) and it always reads hotter initially, and one in the drivers head (controlling the SPAL fan AND giving the stock gauge it's reading).
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

  3. #3
    Registered Member
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    It really doesn't make sense that there would be a measurable difference in the water temperature between the location in the head vs. in the intake near the thermostat.

    But many report that occurs.

    Myself, I wouldn't worry too much about it. Watch for readings that are not normal rather than some specific number.

  4. #4
    Member mech393's Avatar
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    I installed a sensor in the head of my big block and the sensor for my Dakota digital water temp sensor was in the intake manifold there was a 25 degree difference to when my fans would turn on , so I drilled a hole next to the water temp sensor and now the fan turns on at the same as my water temp reads.

  5. #5
    Registered Member 55mike's Avatar
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    I had to use a different fan switch when using the head location vs on the intake. It was a hassle, but I finally found a switch that would close (turn on the fans) at about 210 degrees at the head, which is about 190 at the thermostat. If the wrong switch is used in the head, the fans will run all the time...

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