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Thread: well, the darn thing is out

  1. #1651
    Senior Member pelago's Avatar
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    okay, here goes readings 10 09 am
    motor off cold 20 ohms

    start hi idle 20 ohms

    ten minutes a
    high idle 13ohms

    ten more min 8ohms

    normal idle 8ohms

    while motor running manually adj throttle and got from 8 ohms to 20ohm meter movement, it reacted quite fast to adj of idle. two pictures motor off and one of motor on after running for a while


    zero on meter engione off.jpgafter running for a while.jpg

    ANOTHER GROAN MAYBE I HAVE TWO OTHER GAUGES FROM SAME SOURCE SUPPOSED TO BE ORIGINAL M38A1 GAUGES BUT??? THE BATT INDICATORS IS GOOD BUT FUEL AND TEMP??
    Last edited by pelago; 07-08-2019 at 06:33 PM.

  2. #1652
    Super Moderator bmorgil's Avatar
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    For reference, "Vintage" 12 volt GM fuel and oil pressure gauges use the same sender impedance range. 0 ohms = 0 and 90 ohms = Full scale, a range of 90 ohms. You are only getting a range of 12 ohms. It seems you should see a lot more range?

  3. #1653
    Senior Member pelago's Avatar
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    NO, DON'T AGREE off i 0 ohms, cold running it starts at 20 Ohms and that is with a tested comparison to a mech gauge cold start oil pressure is at 40lbs, 30 min later it is something between 30-40psi????

  4. #1654
    Super Moderator bmorgil's Avatar
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    pelago, it seems as if something must be wrong with the sender or the gauge that's for sure. Can you hook up a mechanical gauge on a "tee" at the block? Maybe you could start it up and compare the two readings just to be sure. Unless its a real good electric gauge, it may not respond the way the mechanical gauge did. Mechanical gauges are very quick to react. Maybe it is reading correctly just, not very fast? As far as the needing a "Tap" to go to zero after you shut it off, that doesn't sound right.
    Last edited by bmorgil; 07-09-2019 at 08:02 AM.

  5. #1655
    Senior Member pelago's Avatar
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    have already done that? a mechanical gauge at junction of oil port with a "T" at start up mechanical gauge went to plus 40lbs psi, electric gauge read 45 (but then again it always reads 45 does not matter if it is off, on or whatever when ignition OFF repeat OFF it reads 45, when ignition turned on it reads 45) however the mechanical gauge reads perfect oil pressure after warm up it reacts to rpm as it should. sending unit is new as already stated several times
    https://www.kaiserwillys.com/oil-pre...-66-m38-m38-a1 this is the sender and it is 24volts

    tap on glass to go to zero?? what can i say you tap on the sob and it goes to zero, turn the freakin switch on it goes to 45lbs motor not running

  6. #1656
    Super Moderator bmorgil's Avatar
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    I think we know the mechanical is telling the truth! It is sure sounding like the gauge and/or the sender is bad. Why not put the old mechanical back in? I would not use the sender or the gauge at this point. It sure is a mystery.

  7. #1657
    Senior Member pelago's Avatar
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    Quote Originally Posted by bmorgil View Post
    I think we know the mechanical is telling the truth! It is sure sounding like the gauge and/or the sender is bad. Why not put the old mechanical back in? I would not use the sender or the gauge at this point. It sure is a mystery.
    EVEN THOUGH THIS HAS BEEN DONE MANY MANY TIMES (MILLIONS PROBABLY) Just dont want some tube coming out of engine that has oil in it, then routing it thru whatever to the gauge... just dont want a chance of line breaking and losing oil

  8. #1658
    Super Moderator bmorgil's Avatar
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    My son feel s the same way! Gotta go with your gut pelago! There are also millions of vehicles running around with electric oil pressure gauges.

    I do know that electric gauges are usually dampened. Perhaps the dampening in the gauge you have is so strong, it just goes up to pressure and sets there. I wonder if it is just flat sticking at 45. It sure seems that way. The fact it stays there after you shut it off, it is looking that way.

  9. #1659
    Super Moderator LarrBeard's Avatar
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    Oil Pressure Gauge; M38A1

    Quote Originally Posted by pelago View Post
    EVEN THOUGH THIS HAS BEEN DONE MANY MANY TIMES (MILLIONS PROBABLY) Just dont want some tube coming out of engine that has oil in it, then routing it thru whatever to the gauge... just dont want a chance of line breaking and losing oil
    I'm going to twist Mike's arm to see if I can borrow a gauge kit to do a science project. Nobody in the M38A1 world seems to really know what does what, especially with NOS senders, repro gauges and adapter resistors.

    Hang in there Ira - help's coming!

  10. #1660
    Senior Member pelago's Avatar
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    damndamndamn double damn, put in the old gauge the original (no idea how old) this one goes to 60lbs and sits there, for insurance purposes i made a 5 point ground jumper cable and ran it to all of the gauges.. ground is ground the world around and continuity on panel is great

    dont care what anyone calls this thing it is nothing but voltmeter, to read oil pressure and it is controlled by a variable resistor called a sending unit
    Last edited by pelago; 07-09-2019 at 10:31 AM.

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