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Thread: 240-Z cooling system adjsustments

  1. #1
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    May 2002
    Phoenix, Az

    Lightbulb 240-Z cooling system adjsustments

    A question for the cooling system experts
    about the indicated water temp on my early '71 240z.
    Referencing Joseph Demers article ,"Steaming Over Your Z" in the summer 2003 issue of Sports Z magazine, I am trying to determine what my temp gage should be reading.
    I have put together a series of resistors equal to 37.3 Ohms which is equivalent to 185 degrees F. according to Dr. Demers and plugged it into the temp circuit to check where the needle on my gage falls, which is one needle width right of center.
    My question to everyone, given that the min gage reading is 120 degrees and the max reading is 250 degrees, would you all agree, or not, that the middle of the gage index is equal to 185 degrees. ( 250 - 120 = 130; half of 130 = 65; 120 + 65 = 185)
    If my reasoning is correct, I have determined that if I add in 5 Ohms to my temp sending unit circuit, the gage should read 185 degrees and be exactly in the center of the gage.
    Sorry for the long post, but I need to have an accurate temp gage in the AZ climate. Thanks for listening and for your help.

  2. #2
    philo "Z" opher Zedrally's Avatar
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    Jun 2002

    Default Re: 240-Z cooling system adjsustments

    Originally posted by AZ-240z

    Sorry for the long post, but I need to have an accurate temp gage in the AZ climate. Thanks for listening and for your help.
    AZ, if you need an accurate gauge then you will need to ditch the Factory Gauge.
    Whilst all the theory is spot on, what most people forget is the actual construction of the gauge itself.

    It is not direct reading nor does it fuction as a normal meter.

    The needle indications are processed [if thats the correct word] bu the heating of a bi-metal metal strip via a heating coil. The fluctuation of the strip then moves the needle.
    Consequently an in-accurate reading of coolent temp is obtained in hot climates due to the ambient temp inside the car.
    Most Zed owners will attest to the in-accuracy of the factory gauge and take any reasonable reading around the centre as "normal".
    Why not just add a digital gauge. There are many kits out in the market that offer an accurate gauge at a reasonable price.
    Mike of the Mire

    73 240Z Rally
    77 260Z Touring

    Bogged but not beaten

  3. #3
    Chillin Inf's Avatar
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    Jan 2003
    Austin, TX USA


    I wonder, has anyone ever found a good swap-out on the temp gauge internals for something more accurate? A digital gauge(or aftermarket for that matter) looks very out of place in a 240z!

    03/72 240Z HLS30-70xxx - R.I.P. 2011/01/04

  4. #4
    beandip beandip's Avatar
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    Mar 2002
    Beaverton, Oregon


    Zedrally , thank you for being able to put it so clearly. These gauges are for references only and are not that reliable. Another thing are you sure the sending unit is right on ? Thats Another question. If you have a clean radiater and the water pump is good , the rad. cap holds the right ammt . of pressure , you should be good to go , as long as you are using coolent. Use the candy thermometer in the rad. test and see what the gauge reads and go from there. None of this is rocket sience and precice.

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