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Thread: VMM Radiator Light

  1. #1
    Join Date
    Sep 2013
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    Anaheim, CA
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    VMM Radiator Light

    I have a 90 SC. My radiator and recovery tank are both full of coolant. Any help as to why my VMM is showing Radiator add coolant light is lit ?

    Thanks Guys

  2. #2
    Join Date
    Jan 2010
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    Bossier City, LA
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    Quote Originally Posted by DougH View Post
    I have a 90 SC. My radiator and recovery tank are both full of coolant. Any help as to why my VMM is showing Radiator add coolant light is lit ?

    Thanks Guys
    The sensor has failed.

    And since they changed the sensor in ... 1993, I think ... we've got hob finding a good replacement, since they used the current through some coolant in the overflow tank (hello, Ford, electrolysis any??) ...

    RwP

  3. #3
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    Dec 2010
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    Zephyrhills F.L.
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    Post in the parts wanted for the sensor or Ck with Ryan at Thunderbird SC Shop.com

  4. #4
    Join Date
    Dec 2007
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    Pacific Rim
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    Might be a simple as cleaning the one you have - remove the wiring connector, then pop it free from the tank. Be aware of a gasket, which may be pretty fragile given the age, etc. Be gentle when removing and handling so as to not fracture the stalk...the weak point is where it joins the top cap.

    The two exposed tangs on the normally submerged probe should be clean/shiny. Scrape off any buildup. Might be a small hole in each one...clear those for good measure. Shine them up w/steel wool and reinstall.

    If you want to experiment, grab an ohm meter and check for continuity from the cap connector pins to each related tang. Gently flex the stalk to check for intermittent breaks.

    Also, note I've gotten false positives from time-to-time and when it wasn't just time to clean the tangs, it took a spare sensor to make things right again. They're not all the same length (and thus resistance), so if you source a replacement, be sure to match same for same.

    Be sure the tank isn't full of sludge while you're in there. Confirm the tube to the radiator's filler neck is clear and the radiator cap is in good shape.

    Still no joy, R & R the VMM (be careful, it's easy to break the plastic that holds the clips) and clean the connector and socket on the back. Still no joy, start inspecting the grounds in the engine bay, starting with the strap from the pass. side motor mount to the body, then the ganged grounds on the header panel near the headlights, then the battery and leads off of it.
    Last edited by KMT; 04-26-2018 at 10:43 PM.

  5. #5
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    Sep 2013
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    Anaheim, CA
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    I have noticed that when the engine is cold at start-up, everything is normal in the VMM. When the engine gets up to operating temperature that is when the low radiator light come on in the VMM.

  6. #6
    Join Date
    Sep 2013
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    Anaheim, CA
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    KMT..........I drained and cleaned the coolant tank. I cleaned the 2 tangs also and the rubber tube to make sure it was clear and clean. When all finished and done I started the engine and the low fluid light cam on like right now. Do those 2 tangs plug into anything in the coolant tank ? They look like 2 prons you put into a wall socket . Seems like they should plug into something but I don't see where at all. I thought io had it fixed but then nothings easy I guess......HELP !......LOL

  7. #7
    Join Date
    Sep 2012
    Location
    Raleigh, North Carolina
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    685
    i just pulled mine out of the tank this week. mine looked like it had two prongs on it too.
    Any idiot can make a Mustang fast...
    It takes a special idiot to make a Thunderbird fast!!!
    89 SC 4.3 stroker 384rwhp 473ftlbs
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  8. #8
    Join Date
    Dec 2007
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    Pacific Rim
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    Quote Originally Posted by DougH View Post
    Do those 2 tangs plug into anything in the coolant tank ? They look like 2 prongs you put into a wall socket . Seems like they should plug into something but I don't see where at all.
    No, they don't plug into anything. They are just bare naked metal prongs that normally sit in the coolant, which conducts just enough current to let the VMM decide if the light should be off, or when the coolant drops, on, as they would then be exposed to just air, which won't conduct electricity, breaking the circuit path.

    Did you wait a few minutes for the system to think about it? Did you ohm the prongs to the connector pins in the top to confirm the circuit isn't broken/failed up the stalk? What happens if you leave the sensor outside the tank, connect a jumper to the pins, then fire up the engine and wait a bit to see if the light doesn't come on? Last time I changed mine out, I had to cycle the key a few times and wait before the VMM cleared and went back to normal operation w/the light off.

    How much residue was built up on the tangs? What did the coolant in the tank look like before you cleaned it out? Is the stalk in good shape with no cracks or breaks?

    Don't fight it...if it's failed, it's failed. If cleaning things up doesn't help, time to source another one. Just do your best to confirm that's the issue.
    Last edited by KMT; 04-27-2018 at 08:11 PM.

  9. #9
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    Sep 2013
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    Anaheim, CA
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    KMT.........To be honest with you. I don't know how to test the sensor. I do have a multimeter though. Is there any way that you can send a link here or explain to me how I do it.

    Thank You

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