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Thread: Bad transmission thermostat=Transmission warning light?

  1. #1
    Join Date
    Apr 2017
    Location
    Thoreau, New Mexico, USA
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    4
    My Cars
    2001 BMW 325xi Wagon

    Bad transmission thermostat=Transmission warning light?

    I have a question: Could a faulty transmission thermostat (the one at the bottom of the coolant expansion tank) cause the transmission light on the dash to come on? It wasn't on until I put the cooling system back together with new parts. I replaced the radiator, hoses, expansion tank, Automatic Trans Thermostat (which arrived with the box all bent and busted), and also had to replace the water pump pulley (I cracked it trying to remove the fan before I ordered the correct tools). I'm guessing the new thermostat was damaged. I didn't see any physical damage to the unit, but could that be the cause of my trans light coming on? I even topped off the transmission fluid just to see, but that didn't fix anything.

  2. #2
    Join Date
    Aug 2014
    Location
    Lawrence Kansas
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    1,236
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    2004 325XI/2008 GL320
    No. The purpose of the trans thermostat is to restrict the entry of antifreeze from the expansion tank to the trans cooler until the engine hits operating temp.

  3. #3
    Join Date
    Feb 2013
    Location
    California
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    202
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    '06 zhp coupe
    OP, you need to scan for codes to see what is really going on.

    dhurley, what if the trans thermostat was stuck closed? Could that make the transmission overheat?

  4. #4
    Join Date
    Aug 2014
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    Lawrence Kansas
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    2004 325XI/2008 GL320
    Quote Originally Posted by Dave1027 View Post
    OP, you need to scan for codes to see what is really going on.

    dhurley, what if the trans thermostat was stuck closed? Could that make the transmission overheat?
    Could, but unlikely given the cooler is still somewhat operational (air) even without coolant circulating through it. I agree, get the trans codes read.

  5. #5
    Join Date
    Aug 2017
    Location
    Kentucky
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    2
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    Bmw, x5 2006
    Did you ever find or fix the problem?

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