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Thread: Temperature guage problem

  1. #1
    Colonel
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    Default Temperature guage problem

    My temperature guage doesn't work. You can take the wire loose from the sender and touch to ground and the guage goes to hot. I just installed the 2nd new sending unit and it still doesn't work. I even installed the 2nd one with no sealant so its brass direct to the engine, still nothing. Any ideas, thanks

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    Colonel eddiec's Avatar
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    check the grounding strapp on the engine. also, run a temperary ground wire9 jumper cables work great) from a bolt near the sending unit to the frame, probably not grounded on the block.
    Eddiec
    1969 m35a2

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    Bet on a clean Corvette rchalmers3's Avatar
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    Thread resurrection warning.

    I have the same symptoms and results that the OP experienced. In addition I have confirmed a good ground path (.3 ohm) between the manifold ground next to the sender, to the battery, the dash plate and the body of the temperature gauge. Grounds all check out.

    TM9-2320-209-20-2-1 leads you through the trouble shooting steps without giving resistance readings for either the sending unit or the meter internals. However the diagnostic steps indicate there is a voltage drop to be expected when the current passes through the meter. To confuse things further, one of the drawings attending the steps is drawn incorrectly, and potentially misleading if you are not understanding the thought process and sequence of the diagnostic routine. The old sender measured 7k ohms at about 50*. The new replacement sender measured 14k ohms at the same temp.

    I have followed the TM for a change ('cause I thought changing the sender would fix it!) and am left with changing out the gauge unit as the solution. I have ordered the gauge, (NOS), and will report my results.

    While I'm waiting for the part to arrive, I'd like to hear the groups thoughts and experiences on this situation.

    Rick

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    4 Star General Guyfang's Avatar
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    Can you list the NSN for the gauge and sending unit? I can try and find the tech data for them.

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    4 Star General dmetalmiki's Avatar
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    Why not just change the electric units for Capillary units?
    All my trucks are fitted with capillary gauges, Oil, And temperature.
    You must surely wonder why all trucks are fitted with capillary Air gauges?
    A solid line requires no earthing, And, "What you see is what you' got".
    Much better. Much safer. At least give it a thought. (As) like mine, the air gauge (Bought from the U.S.) Can be obtained with electrical connectors to Work a Buzzer or Light etc.
    With the option to Activate, low air on, High air on. Very useful.
    Especially with the temperature Gauge.
    Last edited by dmetalmiki; 12-26-2018 at 18:36. Reason: missing sentence
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    Bet on a clean Corvette rchalmers3's Avatar
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    Quote Originally Posted by Guyfang View Post
    Can you list the NSN for the gauge and sending unit? I can try and find the tech data for them.


    Sender is
    6685-00-814-5271
    Gauge is 6685-936-2139

    Thank you,
    Rick


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    Quote Originally Posted by dmetalmiki View Post
    Why not just change the electric units for Capillary units?
    Thanks for the suggestion, I have converted other vehicles to the capillary units, and yes, they operate much more in real time than factory gauges.

    I'm actually not too worried about the temp readings. I have owned this truck for years and am accustomed to operating it without this operational info. But now getting around to fixing some details and I'd like to make it as intended.

    Cheers,
    Rick

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    4 Star General Guyfang's Avatar
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    There is a list of 20 different providers of the part to the Army. If you want a list, can do. There is a list of at least 40 different part numbers. If you want a list, can do. There is a list of 17 different, (cancled) NSN's. If you want a list, can do.
    Sender:

    THREAD LENGTH 0 383/500 INCHES NOMINAL
    OVERALL LENGTH 2 82/125 INCHES MAXIMUM
    OUTSIDE DIAMETER 0 3/8 INCHES MAXIMUM
    OPERATING TEMP RANGE +48.9/+160.0 DEG CELSIUS
    MOUNTING FACILITY SCREW THREAD SERIES DESIGNATOR UNS
    UNIT TYPE PROTECTIVE TUBE
    MOUNTING FACILITY TYPE AND QUANTITY 1 THREAD
    MOUNTING THREAD QUANTITY 14 PER INCH
    MOUNTING FACILITY NOMINAL SCREW THREAD DIAMETER 0 1/2 INCHES
    DISTANCE ACROSS WRENCHING SURFACE FLATS 0 469/500 INCHES NOMINAL
    ACCOMMODATED CONTACT TYPE AND QUANTITY 1 MALE SNAP-ON
    MATERIAL STEEL CORROSION RESISTING OVERALL
    STYLE DESIGNATOR TRANSMITTER, 24V DC
    TERMINAL TYPE AND QUANTITY 1 THREADED STUD


    There is a list of 15-16 providers of this part. There ias a list of 13-15, (canceled) NSN's. There is a list of 22 part numbers for this part. Can provide all this info if needed.

    Gauge:

    SCALE MARKING AND SURFACE FINISH NUMERALS NONLUMINOUS
    DIAMETER 2 INCHES NOMINAL
    SCALE DIVISION QUANTITY 4 SINGLE INDICATOR SINGLE SCALE
    CURRENT TYPE DC
    DC VOLTAGE RATING 24 VOLTS NOMINAL
    DEPTH 2 3/8 INCHES NOMINAL
    CONTACT QUANTITY 2
    CONTACT TYPE SCREW
    PRESENTATION TYPE DIAL
    SCALE RANGE +120.0/+240.0 DEG FAHRENHEIT SINGLE INDICATOR SINGLE SCALE
    ELECTRICAL CONNECTION QUANTITY 2
    ELECTRICAL CONNECTION IDENTIFYING NUMBER MS33800
    POINTER TYPE INDICATING SINGLE POINTER
    MOUNTING FACILITY TYPE AND QUANTITY 1 CLAMP
    TEST DATA DOCUMENT 81349-MIL-I-10986 SPECIFICATION (INCLUDES ENGINEERING TYPE BULLETINS, BROCHURES,ETC., THAT REFLECT SPECIFICATION TYPE DATA IN SPECIFICATION FORMAT; EXCLUDES COMMERCIAL CATALOGS, INDUSTRY DIRECTORIES, AND SIMILAR TRADE PUBLICATIONS, REFLECTING GENERAL TYPE DATA ON CERTAIN ENVIRONMENTAL AND PERFORMANCE REQUIREMENTS AND TEST CONDITIONS THAT ARE SHOWN AS "TYPICAL", "AVERAGE", "NOMINAL", ETC.).
    SPECIFICATION/STANDARD DATA 96906-MS24543 GOVERNMENT STANDARD
    FSC APPLICATION DATA TEST SET,ELECT. EQUIP.

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    Bet on a clean Corvette rchalmers3's Avatar
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    Guy, thanks for all the manufacturer and physical data on the parts. At this moment, I don't think that info is of use to me. I have learned in the past that gauges can be surprisingly complex inside. Often gauges are built with internal circuitry to make them deflect slowly, sit in one position over a wide temperature range and remain stable. Therefore, even if we could find the resistance reading across the meter, I'm not sure that info would be useful. I thought I'd ask anyway 'cause I'm constantly discovering how much I don't know.

    Rick

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    I thought I'd follow up on this thread after "fixing" the issue. The best reason I can give as to why the temp gauge now works is that I touched everything. I had replacement sensors and gauges fitted, then went back to my original pieces and voila! Probably I had missed a cruddy connection somewhere and restored a ground contact, even after taking care to measure things. In the course of doing all this, the oil pressure gauge also now reads correctly, something I was going to tackle subsequently.

    I have two pieces of info to leave here, followed by a few musings:

    First is that the two temperature sensors I have measured from 7-10k ohms at 50*, and about 1k ohm at boiling. I hope this data helps someone now or in the future.

    Second is that the internals of the gauge are exceedingly simple. There are two coils in series and a simple needle movement. I didn't measure the resistance across the meter. Best to follow the TM and confirm/deny the existence of the voltage drop.

    I bought a NOS meter for a replacement, thinking that the metal gauges are more robust. Turned out the NOS gauge was BIB (broken in box). I was dubious it was going to work because it had zero resistance across the contacts and did not drop the voltage to the sender as the TM instructed. So I installed it and confirmed it was kaput at the get-go. There was a very fine wire connection inside that is broken and will be difficult to patch.

    My deuce really is cold blooded. I can block the radiator completely, drive it around (unloaded) on surface streets in 60* weather, and it won't broach 170* operating temperature. I think it's time to check for the existence of a missing or stuck open thermostat. Onward and upwards.

    Rick
    Last edited by rchalmers3; 01-11-2019 at 22:29.

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