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Thread: How to change the water sensor for the water temperature gauge (#102450)?

  1. #1
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    How to change the water sensor for the water temperature gauge (#102450)?

    Hi!
    I need to change my first inaccurate and now not-reading water temperature sensor, located at the rear right end of the engine block.
    I am a little afraid, what happens if I screw the sensor out. Do I have to expect some/a lot of water to drain out of the sensor hole from the block? Do I have to bleed the water cooling system after changing the sensor?
    Or is this just half as problematic as I think it is? Maybe someone has already changed this sensor before (I would expect this ) and gained experiences?

    Thank you very much and best wishes from cold Germany,

    Lars.

  2. #2
    Senior Member 82DMC12's Avatar
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    Quote Originally Posted by larsmhh View Post
    Hi!
    I need to change my first inaccurate and now not-reading water temperature sensor, located at the rear right end of the engine block.
    I am a little afraid, what happens if I screw the sensor out. Do I have to expect some/a lot of water to drain out of the sensor hole from the block? Do I have to bleed the water cooling system after changing the sensor?
    Or is this just half as problematic as I think it is? Maybe someone has already changed this sensor before (I would expect this ) and gained experiences?

    Thank you very much and best wishes from cold Germany,

    Lars.
    Yes, the overflow tank will empty out through the hole where the sensor was as well as whatever it takes to drop the block level down to the hole as well. If you haven't changed the coolant in the last two years, you should just do it now. Loosen and disconnect the lower coolant pipe hoses near the transmission and drain everything down from there. If you don't want to spill anything from the sensor hole, you're going to have to pull one of the block plugs as well. the one on the driver side is easier to get to.

    I'd want to drain everything down before replacing the sensor because I don't like getting coolant stuck in the Valley of Death.
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!
    Total frame-off restoration completed 2021-2023

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Kansas City

  3. #3
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    Hi Andy!

    Thank you for your answer!

    The new sensor arrived today and I will check it, before I will put it in. But now I know that it might get hard to change it...
    I will write a report, when I did it (I think I will wait for the weekend...).

    Best wishes,

    Lars.

  4. #4
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    If you do it real quick you won't lose much. Take the old one out, stick your finger over the hole and then quick put the new one in. You shouldn't lose much and you don't have to bleed afterwards. If your coolant looks or smells funky, if it tests high on PH or is not good to -20 F (or is over 5 years old) it should be flushed out and replaced anyway. The temp sensors don't go bad so much, usually when they go bad it is either because you ran with very low coolant or you overheated the motor. More likely it is just a dirty connection. Change it and see if that fixes you up.
    David Teitelbaum

  5. #5
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    Quote Originally Posted by larsmhh View Post
    Hi Andy!

    Thank you for your answer!

    The new sensor arrived today and I will check it, before I will put it in. But now I know that it might get hard to change it...
    I will write a report, when I did it (I think I will wait for the weekend...).

    Best wishes,

    Lars.
    Lars,
    Consider doing a temperature test before installing the sensor. This is similar to what you might do when checking a thermostat. If you have a portable hot plate, pot with water, and thermometer; you can connect the sensor to the car (An extension wire can be used). Secure the sensor in the pot so just the sensing element is in the water. Turn on the hot plate and compare the pot thermometer with the instrument cluster readout as the pot heats. Eventually the pot will stabilize at boiling temp (~212 degF). Now verify what the instrument cluster reads. Even though the critical temperature during normal operation with your car will be 10 to 15 degrees higher (depending on pressure cap and antifreeze concentration), its good to have a reference to a known value just to understand if your cluster temperature reading is high or low by X amount. Plus, it verifies it's working before you make all the effort to install it.
    Ron

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    Quote Originally Posted by David T View Post
    If you do it real quick you won't lose much. Take the old one out, stick your finger over the hole and then quick put the new one in. You shouldn't lose much and you don't have to bleed afterwards. If your coolant looks or smells funky, if it tests high on PH or is not good to -20 F (or is over 5 years old) it should be flushed out and replaced anyway. The temp sensors don't go bad so much, usually when they go bad it is either because you ran with very low coolant or you overheated the motor. More likely it is just a dirty connection. Change it and see if that fixes you up.
    I was able to replace my temp sender this way, and I didn't lose too much coolant.

  7. #7
    Senior Member Rich's Avatar
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    Quote Originally Posted by dmc4087 View Post
    I was able to replace my temp sender this way, and I didn't lose too much coolant.
    And an old towel below the sensor port can keep most/all of the leaking coolant under control during the sensor replacement.
    March '81, 5-speed, black interior

  8. #8
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    Hi,
    I wanted to write a summary, how the case went on.

    Thank you for the hint to check the (old) gauge and/or the (new) sensor about their cooperation due to the exchange!!!
    The new sensor reads 320 - 340 Ohms at 100 C boiling water, but my gauge just wants 90 - 95 Ohms to show 104 C equal to 220 F.
    This means, the new sensor will also not work propperly in my car!

    I then used a potentiometer and collected the correct resistance to show the 4 landmarks of the gauge.
    I found a website from VDO instruments, which offers a lot of different sensors for their water/oil/gas/... gauges and shows tables with temperature vs. resistance. (https://vdo-webshop.nl/de/34-temperaturgeber?page=1)
    I found a sensor that fits in principle, if I add a resistor of 40 Ohms to its measurements. It is the VDO A2C1755260001

    Next problem: It does not look like our sensor #102450 and the thread does not fit. I do not really know, what kind of thread the PRV-engineers used. The one that may fit is a metric one (M14) with a pitch (<- is this the right word?) of 1,25, which VDO does not use (they use a lot of M14, but a pitch of 1,5).

    So I talked to a turning shop. They suggested to buy a sensor with a thread of M16 and then they will try to thred a M14x1,25 to the sensor. This can be done at earliest in january 2023...

    I am still waiting for the new M16 sensor to arrive and so I will report, if I have more news about this story...

    Does someone know the real thread of our Delorean-sensor? Is it really M14x1,25 or maybe a british or american thread? The nut I used for testing fits and turns easily, but maybe a little too easy!? There is a large clearance...

    Best wishes,

    Lars

  9. #9
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    This is the sensor #102450 and the nut M14x1,25, that fits onto the thread of the sensor. But I?m not sure, if this is the original thread or if it simply fits...
    Attached Images

  10. #10
    Senior Member Bitsyncmaster's Avatar
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    If the nut fits on you probably have the correct size (a lot of slop would not be correct). There are different specs on the threads of some nuts and bolts as far as how tight they mate.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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