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What does the coolant temp sensor do on an 85' QV?

Discussion in 'Technical Q&A' started by 308GTS, Feb 20, 2004.

  1. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    What exactly does the coolant temp sensor do on an 85' QV? What does it send power to? Mine is a closed circuit when cold and open when warm? It is set up different than on an 83' QV as it sends power differently. How does this system work? Thanks.
     
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  3. stevej33

    stevej33 Karting

    Feb 16, 2004
    76
    Lincoln, UK
    Full Name:
    Steve Jollands
    if its anything like my 84' mondial it should kick the fans into action when it gets hot.

    steve j
     
  4. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    308GTS -- Can you clarify which "gizmo" you're asking about:

    1. The thermo-switch in the radiator (per steve j's response),

    2. a different thermo-switch, or

    3. the NTC thermo sensor?

    (you kind of mixed together the "switch"-"sensor" lingo in you post)

    If it's #2 -- it's usually used on the Lambda-equipped CIS systems to somehow "tell" the control system to run open-loop (i.e., to ignore the O2 sensor voltage output and run using the mechanical and electrical defaults). Do you have the schematic?
     
  5. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    Coolant temp sensor not thermo switch. It is a small sensor on the bottom of the 308 recovery tank used in conjunction with the Bosch CIS System.
     
  6. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    I don't think it is for the lambda sensor as the 83' QV has one but has no 02 sensor. I have a schematic yes but is it readable no, the lines are broken and not useful hence my question here.
     
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  8. Steve Magnusson

    Steve Magnusson F1 World Champ
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    "Lambda sensor" is usually used as a synonym for "O2 sensor" -- are you saying that your OM specifies both an O2 sensor and a (different) Lambda sensor?

    You're using the word "sensor" even though you talk about the device being "open" or "closed" -- is it a switch or a variable resistor?
     
  9. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    I know that but an 83' QV doesn't have an 02 sensor hence it does have a coolant temp sensor. Typo. Meant to say that the 83' has no 02 sensor but has a coolant temp sensor. Plus the 83' has no ECU to communicate with about open/closed. Now the 85' does but back to my question what does the coolant temp sensor do and where is power sent? I am assuming it diverts power when cold but since it is on both year cars it must serve to divert power differently. Why? That is part of my question also.
     
  10. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    No that was a typo on my fault. I will only use 02 sensor from now on. 84-85 308s are the only 308s from the factory with 02 sensors.
     
  11. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Your original question title was about your '85 (with O2 sensor) right?

    Although the '83 308QV also has a thermo-switch in the coolant tank, I believe that it's used for controlling the cold start air valve (a gizmo which your '85 does not have) -- see page 68 in your '83 US OM.
     
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  13. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
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    Ok. So on the 85' it is used for closed/open but does it divert power to the AAV or is it only used for ECU/02 sensor?
     
  14. Steve Magnusson

    Steve Magnusson F1 World Champ
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    I believe +12V power is always supplied to the internal heater of the Auxillary Air Valve (AAV) with the engine running, but now you're getting to a detail that requires the schematic to check.
     
  15. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    Thanks for the info. I appreciate it. If I could read it I would be happy to but I am going to work on getting a blown up one.
     
  16. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Check page 75 of the 307/84 OM -- it shows just the injection system wiring schematic for the K-Jetronic with Lambda system. Also, reading the nearby text, it indicates that the "pulse" air injection system is only active during cold-running -- I would also guess that the signal from the thermo-switch in the coolant tank is used for this control too (i.e., cold = switch contacts closed = run air injection system; warm = switch contacts open = turn off air injection system)
     
  17. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    True. I would say that is correct. I didn't even think about it being part of the pulse air injection system. I wonder too if it doesn't tell the ignition ECUs to advance the timing when cold.
     

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