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Mystery USA-only temperature sending unit

Discussion in '308/328' started by dave80gtsi, Jun 24, 2005.

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  1. dave80gtsi

    dave80gtsi Formula 3
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    Dave Meredith
    #1 dave80gtsi, Jun 24, 2005
    Last edited by a moderator: Sep 7, 2017
    Greetings to all - Does anyone know, with certainty, the function of this specific coolant temperature sensor which is mounted to the face of my thermostat housing? The car is a USA spec 1980 308 GTSi, and looking at the same year's Euro parts book, there is no such sensor at this location, so this is unique to the USA market. Translated into English, the item description in the USA parts book is "thermostat command injector starter", which is a bit vague. My first thought was that this controlled that obnoxious stone cold engine fast idle feature, but the sensor for this dubious function is mounted to the coolant expansion tank, so that's not it. Any one know?

    Thanks and Cheers - DM
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  2. carlrose

    carlrose Formula Junior

    Nov 25, 2003
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    #2 carlrose, Jun 24, 2005
    Dave I'm going to take a true stab here for you:

    On my 328, an identical-appearing switch is the temp sender for the FI (only) have one black & one purple wire leading into. Functions to "signal" the FI ECU coolant is warm.

    Goodness I feel foolish for posting but hope it helps. Mine is marked "8923" and "9055" and "57/33" on successive hex faces. Part # 121777.

    :) Carl
     
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #3 Steve Magnusson, Jun 24, 2005
    Dave -- What are the wire colors that are attached to the device? If they are both RV (red/green), it is a thermal SPST switch (closed cold and open warm) that is in series with the cold start injector coil (i.e., when warm, the cold start injector is prevented from firing regardless of what else is going on in the system) per the 216/81 OM (Item 106 "Cold Start Thermoswitch" on the schematic)

    The '80-'82 308i US SPC at FerrariUK shows it as PN 115652, and, as you noted, it's not used on the standard '80-'82 308i.
     
  4. dave80gtsi

    dave80gtsi Formula 3
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    #4 dave80gtsi, Jun 27, 2005
    Steve - Apologies for getting back to you late on this one, but I couldn't check the wire colors until just this a.m.

    Yes, the wires are indeed both red/green, so your info seems correct. Many thanks!

    But, now the puzzle: Why use this switch in the first place? From your explanantion, it seems redundant. Further, why use it for USA cars only and not Euro? Doesn't sound like one of those weird USA "smog things" to me!

    Cheers - DM
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #5 Steve Magnusson, Jun 27, 2005
    No problem Dave, but your US version does have a more complicated electrical system wrapped around the K-Jet system (with electrovalves for EGR control, air injection diversion, and fast idle control that aren't on the Euro) -- but I'm not sure that those extra things directly necessitate the extra thermoswitch on the cold start injector.

    It could just be an extra safety precaution -- i.e, a cold start valve "open" malfunction (for any reason) on a cat-equipped US 308i is a fire hazard; whereas, it's not on a cat-less Euro 308i -- just a guess...
     

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