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Thread: Need help understanding hydralic fan setting 5.7 hemi

  1. #1
    Potential Tuner
    Join Date
    Nov 2021
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    1

    Need help understanding hydralic fan setting 5.7 hemi

    I just picked up this unit to help adjust the fan speeds on my 09 Jeep Grand Cherokee with the 5.7l hemi. The factory settings seem really high and after a new winch and bumper set up my coolant temps at idle after cruise (ie stop lights, drive thru, etc) get pretty high before the ECU does anything about it. I changed the coolant, thermostat, purged the air but didn't make much difference.

    Going through the ECU file it does look that the set points for the fan to come on are very high, over 230 degrees in most circumstances. I planned on changing the trigger points for the low, middle, and high fan settings to 205, 210, and 215 respectively. Here are my questions:

    There is a section for PWM desired temp. Stock was set to 218 deg. How does this factor in to the low mid and high speed trigger point settings?

    The hysteresis values are a bit confusing to me. If I understand correctly, this is the temperature drop through which the fan will stay in the triggered mode. So lets say stock, the low speed fan at low vehicle speed and a/c off is set to 230 degrees and a stock hysteresis of 37.8 degrees, that the fan will come on at its low speed at 230 degrees but keep spinning until the coolant temp is down to 191.2 degrees?

    If I am correct about the above, why is the low point for adjustment so high on this? The lowest setting is 32 degrees, high goes up to 491 degrees.

    Thanks for helping me understand.

  2. #2
    Potential Tuner
    Join Date
    Feb 2021
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    5
    Just saw this.

    Barra, I believe that on Grand Cherokees like ours (mines a 2010 5.7), the "PWM desired temp" is the only thing that controls the hydralic fan.

    I have a 180 T-stat and set the "PWM desired temp " to 199. On a hot day I let it idle until the fan came on. It came on at 199.

    I suspect, but have not confirmed, that the fan turns faster as the temp goes up to try to bring the temp back to 199.

    You might want to play around with this and see what happens.

    Andy

  3. #3
    Tuner
    Join Date
    Jan 2021
    Location
    Cape Town
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    Barra, yes the hysteresis is like the upper and lower spec of the temp range. It is important to set the low, med and high speeds. I have a 88degree C thermostat and high @103C, medium @98C and low @95C with PWM desired @ 94C. The fan will thus run at different speeds with full speed @ 103C.
    2010 Jeep GC 5.7 Eagle Head motor, 2" OME lift, cats removed, full MDS delete