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Thread: well, the darn thing is out

  1. #1641
    Super Moderator gmwillys's Avatar
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    Often times, the harnesses would last a lifetime, unless the Jeep was subjected to salt. Sea salt or road salt from the Midwest, would deteriorate the harness. Good wire is expensive, but worth every penny. Your expertise on wiring boats was worth every penny as well.

    The oil pressure gauge you are using is the original gauge you had when first starting the engine after rebuilding? If nothing else has been changed except for the sending unit, then the sending unit is retaining pressure when none is applied. If the gauge wasn't used until now, then the gauge itself may be hanging up at 45 psi, and won't go down to zero.

  2. #1642
    Super Moderator LarrBeard's Avatar
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    Oil Sending Unit

    Quote Originally Posted by pelago View Post

    new issue, new oil pressure gauge. new sending unit, good hookup, good wire, sits there at 45 does not go to zero when ignition turned off????
    Not unusual - senders and gauges don't match very well. I replaced the sender on the truck and with engine off it read about 15# , running about 50#. I know at cold idle it was about 30# on mechanical gauge.

    It took 8.2-ohms in series with the gauge to get it to settle at 30# running, close to 0 engine off. I'll send you an 8.2 ohm resistor - I bought several, plus some other stuff, just to justify shipping. Your gauge and sender may be a little different, so if this does't exactly work, juggle values a little.

  3. #1643
    Senior Member bmorgil's Avatar
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    Here is a good diagnostic. Helps out with the correct readings for all electric senders. I think they might be talking 12 volts however. You will have to convert the readings to 24 volt I think?

    http://www.precisionspeed.com/technical-support/

    This is an excerpt from it. I hope this isn't it!

    b) Pointer resting at some point well above minimum dial scale reading, but not stuck at full CW (off-scale). Replace gauge. This is an abnormal condition that should not occur and could only be caused by a fault within the gauge or damage to the gauge caused by the application of an excessively high input (power) voltage or subjecting the gauge to extreme environmental abuse. Once again the cause of the failure should be investigated.
    Last edited by bmorgil; 07-06-2019 at 04:13 PM.

  4. #1644
    Senior Member pelago's Avatar
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    what is confusing is that with a mechanical guage and tubing hooked right at the oil port i read terrific oil pressure and the meter moved with rpm, this darn thing goes to 45lbs and sits there no movement at all, kinda discouraging all of it is new?

  5. #1645
    Super Moderator LarrBeard's Avatar
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    Oil Gauge/Sender

    Quote Originally Posted by pelago View Post
    what is confusing is that with a mechanical guage
    Forget my suggestion about fixing an electric gauge....

  6. #1646
    Super Moderator gmwillys's Avatar
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    No electricity needed here. I know he had a gauge on the engine on start up, but wasn't sure if it was the original gauge, or a new one, etc. There must be a link or restriction in the tube.

  7. #1647
    Senior Member bmorgil's Avatar
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    Quote Originally Posted by LarrBeard View Post
    Forget my suggestion about fixing an electric gauge....
    Forget the diagnostic on electric senders.....

    pelago, I am not quite clear. Are you saying the old gauge had more movement than the new set up? Or, Did you test the new gauge outside the dash and it was fine. Then the new gauge seems stuck after you put it in the dash? If after you put it in the dash, the tubing from the block to the gauge got pinched, kinked or bent to sharply, that would make the gauge act like you are describing. Is the tubing from the block to the gauge plastic? If it is, that stuff is notorious for kinking with the slightest provocation.
    Last edited by bmorgil; 07-07-2019 at 06:29 AM.

  8. #1648
    Senior Member pelago's Avatar
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    i think i might have confused some here. when i turn the ignition switch on the gauge goes to 45lbs, when i start the motor it never changes, something wrong here this should not be, when i turn engine off i tap on the gauge and it goes to zero?? the gauge in question was from a supply house in wisconsin and was new in the box. when i was first starting on the engine i had a old mechanical guage in the jeep it was hooked to the oil port by a tube and had fantastic oil pressure.. when motor started it would be in high forties and when it warmed up it would stay at 40+ - amd the oil presssure reacted to the rpm of motor. only other guage i have is the original and no i have not tried it. review. new gauge, new wire, good voltage correct connectors, new gauge , new sending unit 0-60psi sending unit, turn switch on it goes to 45lbs, start motor no movement at all, tap on glass and nothing stop motor and tap on glass it goes to 0

  9. #1649
    Senior Member bmorgil's Avatar
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    That sounds like a bad gauge.

  10. #1650
    Super Moderator LarrBeard's Avatar
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    I’ve had a weekend to think about your oil gauge problem and I wonder if you have an issue because you have a gauge for a 6-volt or 12-volt system and you are using it on the 24-volt M38A1.

    As I look at the various M38 Forums, I see a lot of chatter about gauges and sensors. It looks like somewhere in the M38A1 production, the gauge was changed from a 60 PSI gauge to a 120 PSI gauge. There are conflicting opinions about compatibility of 60 PSI and 120 PSI system components. Some folks seem to think if you put a 120 PSI gauge onto a 60 PSI sensor, you will read the actual oil pressure (just low on the gauge) and others think the gauge will read twice the actual pressure.

    I look at the KWAS catalog and I see that the oil pressure gauge kit (KWAS P/N 647054) has a sensor, gauge and two different resistors in the kit.

    https://www.kaiserwillys.com/instrum...a-3b-m38-m38a1

    I haven’t bought this kit, but I’d wager that the gauge is a repro gauge that is basically a 6-volt gauge with one dropping resistor for 12-volt systems and another for 24-volt systems. It claims to use an original sensor, but it does not say if it is a 60 PSI or 120 PSI sensor.

    In your case, I have a guess what is happening. You do not mention a dropping resistor for the gauge. The gauge you bought may be basically a 6-volt gauge. When you hook it up to 24-volts on one side, the sensor on the other and turn on the ignition – you pin the gauge full scale plus. (You may not have done this with your Simpson 260 – but I have done it to mine). If you peg the needle, it sticks. Peck on the glass and it returns to zero. Since the gauge is still working, you probably have not burned it out – yet.

    If you have some radio buddies, try to find a 100-ohm, 5-watt wire wound variable resistor. Set it to 100-ohms, put it in series with the gauge and sensor. Turn on the ignition, the gauge should sit at zero. Start Max Magoo up. The gauge may not read anything at all, it may read a little or it still may be high- but not pinned. If it reads nothing or low, reduce the resistance until you get your normal cold idle oil pressure. If it reads high, we’re on the right track, just not enough resistance yet. Let it warm up and see where the pressure on the gauge goes. You might put a tee-fitting on the oil port for a cross check with a mechanical gauge.

    Once you have the variable resistor set where it looks right, measure it and install a fixed series dropping resistor behind the gauge. That is what the KWAS kit seems to be doing.

    You would do a great service to the forum if you would do a little science project for us. Could you take the Simpson 260 and measure the sensor resistance with engine off, then measure the resistance with the engine at cold idle, hot idle and at hot cruise engine RPM. No one seems to know that simple answer and it would help us with the next guy’s problem.

    Good luck and keep on spoiling Jake!

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