Do the cooling fans have a turn off at speed?

Discussion in 'Engine & Drivetrain' started by SnowDrifter, Sep 30, 2018.

  1. SnowDrifter

    SnowDrifter Full Access Member

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    Just curious if the efans turn off at a given speed like 30mph or something, or if it's based exclusively on coolant temp
     
  2. swathdiver

    swathdiver Full Access Member

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    This is from gleaning my GMT900 shop manual:

    The ECM commands the low speed setting ON under these conditions:

    - ECT reaches about 202 degrees.
    - AC Pressure exceeds 210 PSI
    - After the engine shuts off, if the coolant is greater than 214 degrees the low speed fans will run for at least a minute. At the end of this minute, if the ECT drops below 214 the fans will shut off. They will shut off after 3 minutes regardless of temperature.

    The ECM commands the high speed setting ON under these conditions:

    - ECT exceeds 220 degrees
    - AC Pressure exceeds 265 PSI
    - When certain DTCs set.

    While idling and at very low speeds, the fans are only allowed to speed up if required to maintain idle stability and keep them from cycling back and forth.
     
  3. Doubeleive

    Doubeleive Elite Member Supporting Member

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    that's interesting because I don't see how the fans running (blowing air on the radiator) after the engine is shut off would somehow cool the temp sensor on the engine bock?
     
  4. SnowDrifter

    SnowDrifter Full Access Member

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    Hmm.. Was hoping for a way to set the fans up automatically to stay on in traffic to blow air over the various components in the engine bay even if the coolant is OK

    So: Alternate idea

    looking at the diagram, it appears as though I could wire a switch of one form or another to complete the ground for the relay's trigger for all 3 fan relays to trigger them into "high". Would need to diode isolate each of them so as to not interfere with stock functionality when the switch is "off"

    Or I could do the same with a 3 position switch and allow for toggling between stock - low - high. Would need to think about the most appropriate way to wire that one
     
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  5. SnowDrifter

    SnowDrifter Full Access Member

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    upload_2018-9-29_23-15-51.png
     
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  6. HiHoeSilver

    HiHoeSilver Away!

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    The fans don't blow on the radiator, they pull air through the radiator and blow air on the engine.
     
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  7. Doubeleive

    Doubeleive Elite Member Supporting Member

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    ok that would make sense, lol, I don't know what I was thinking :confused:
     
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  8. SnowDrifter

    SnowDrifter Full Access Member

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    Sanity check anyone? Does it look like manually triggering all 3 relays would do what I want?

    Current idea is with a 3 position switch.

    Position zero will be stock. There's no ground circuit completed

    Position 1 will be low speed. It will ground out fan relay 1

    Position 2 will be high speed. It will ground out all 3 fan relays

    upload_2018-9-30_12-44-32.png

    This look right?
     
  9. adriver

    adriver Full Access Member

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    Just curious why. You don't want to run your engine cooler than normal operating temp, and this sounds to me as if: all you would be doing is heating your engine bay up further by moving more hot air and causing more heat transfer to occur throughout the engine bay... This sounds like its a 130 degrees out, and you think you are going to cool yourself off by blowing a hair dryer on you because its only blowing 115 degrees.
     
  10. SnowDrifter

    SnowDrifter Full Access Member

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    That's not at all how this works
     

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