first road construction / over heat of the year

Discussion in 'KJ General Discussion' started by XWrench3, Apr 8, 2021 at 7:16 AM.

  1. XWrench3

    XWrench3 Full Access Member

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    well, we found the first of MANY road construction /repair projects of the year (just the first one WE hit, the state starts them much earlier). and we were stuck there long enough that the coolant began to boil, and that is NEVER good, but twice as bad on this engine type (3.7l). so what i want to do is add a toggle switch , zener diode, and hot wire up to the electric fan. but having poor (hey, at least i own up to it) electrical skills, I am not certain exactly where to place the diode to prevent the 12v power to back feed into the computer. I'm also going to have to ask about replacing the engine cooling fan switch, and or coolant temperature (gauge sending unit), because the temperature never indicated hot at all. it showed exactly where "normal" operating temp always is. from what i can see in the service manual, the coolant temp sender appears to be the only temp sensor from the engine. so if that is the case, it makes sense that the fan never turned on.
     
  2. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    I'd be replacing the coolant temp sensor first with a mopar one. That may be the issue.
    Anytime you turn on the A/C the electrical fan should come on, is it working correctly? You have a 2 speed electrical fan, hi/low.
    Next is cooling fan relays swap them around & see if that helps.
    There are a couple of threads re adding a toggle switch with PCM, I'll have to try to find them later.
    1 is post #6: https://www.jeepkj.com/threads/help-fan-relay.57994/
     
  3. turblediesel

    turblediesel memberable

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    A zener-diode!

    How about a double-pole single-throw switch (2 position switch with 4 lugs) to switch the circuits and keep them seperate at the same time. Or use a double-pole double-throw switch (3 position switch, middle off with 6 lugs).
     
  4. Billwill

    Billwill Full Access Member

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    What turblediesel and LibertyTC said ^^^

    You ideally need to fix your basic overheat issue first before adding Overide switches... which I would definitely do for emergencies if I had an Electrical Cooling fan...I only have a Viscous Fan on my 2002 Export CRD.

    Definitely not a Zener Diode!
    These are purely for voltage regulation ie. if you say needed a steady 9 volts to drive some 9 volt gadget in the Cabin you would fit a resistor in series with a 9 Volt Zener Diode in reverse polarity to the battery ie. the Diode would not be conducting.
    Your 9 volt gadget would connect across the diode while the remaining 3 volts gets dropped on the resistor...bit of a waste of power!

    Not important...lets just get the overheating problem fixed first and then we can discuss Overide Switches.;)
     
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  5. XWrench3

    XWrench3 Full Access Member

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    well, i'm finally over Covid 19, and got a chance to look at the jeep today. i did the first suggested check, which was to see if the cooling fan works when the a/c is turned on. and it does, but kind of funny. when i turn the a/c on, at normal operating temp (200-205 ish by a Sun mechanical gauge) the fan runs for about 5 seconds. as the engine temp goes up, the fan runs on-off-on increasing infrequency as the temp climbs. but never turns on and stays on. i disconnected the fan power coupler, and tried jumping power to it directly. only one speed works. but i'm not sure how to tell which speed that is. my gut feeling is low, since the engine previously got hot enough to boil the coolant. im going back out now to see about swapping relays. but with only one fan speed, i'm not sure if that will make a difference.
     
  6. XWrench3

    XWrench3 Full Access Member

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    well, i have a set of "J"hooks (electrical tool that pierces the wire without slicing thru the insulation). i pierced the center wire of the fan side of the harness (black) with the negative side of my multi meter, then pierced the high speed side, and it is always hot (with the engine running). no fan rotation. so i pierced the low speed side, and it turns on when the low speed fan relay clicks on. so it appears that it is the low speed side of the fan is the side that works. great. what is weird, is i can remove the hi speed relay completely, and there is still battery voltage there. which is probably why the hi speed side of the fan no longer works. but how is power getting to the fan with the relay removed? as far as the coolant temp sensor goes, i can not throw $85.00 at a "maybe".
     
  7. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    I don't know if this may help, but I recently tested my fan set in heat mode only, and hooked into OBD2 port with Scangauge.
    Fan came on while parked at 219F and shut off as it cooled down, at 214F= normal.
    Only in summer have I heard the high speed come on, and it did not last long.
    Jeep seems to like it running hotter than most of us would like.
    The dash Temp gauge is a "dummy gauge".
    At the half way point your coolant temp is between 178 degrees and 229 degrees, at 3/4 your temp is 230 to 259 degrees, and at full hot your above 260 degrees.
    Do you have an OBD2 scangauge ?
     
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  8. XWrench3

    XWrench3 Full Access Member

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    yes, i have a scan tool. it shows a bad o2 sensor. but nothing about the cooling system, even after the overheat issue.
     
  9. XWrench3

    XWrench3 Full Access Member

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    i was just thinking, that the temp gauge in the dash NEVER goes higher than 1/2 way up.
     
  10. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    Get that NTK 02 sensor fixed. Don't want to damage cats.
    I have a scan tool & hidden OBD2 gauge pack reader combined.
    You need to reference your Water temp against the actual dash idiot gauge. The stepper motor could be out to lunch.
    Here you can see the actual OBD2 reporting Fahrenheit Water Temp (fWT) 219 degrees.
    [​IMG]
    https://www.scangauge.com/products/scangauge-ii/
     
  11. Billwill

    Billwill Full Access Member

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    Ok XWrench3 you are doing all the right things as far as the relays on the cooling fan are concerned but as I stated before...there are weird things going on in that area which I do not fully understand...been into these logic diagrams before!;)

    So Page 8W-30-22 in the 2005 Jeep KJ Service Manuals shows the 2 relays....Slow Speed Relay powers the fan motor via Dark Blue/Dark Green Wire while High Speed Relay supplies voltage via the Dark Green/Dark Blue wire.

    Black is ground at G112...hopefully that is there!

    The PCM powers the two relay's ground side of the coils on the relays.

    I have a suspicion that if you pull one of the relays out the PCM might sense that this has happened and might make changes to how it drives the other relay!:confused:

    So without pulling out any of the relays you could try swapping over the Dark Green/Dark Blue wire with the Dark blue/Dark Green wire at the Fan Motor plug. In other words you should have High Speed Fan when Low Speed Relay is energized and High Speed Fan when Low Speed Relay is energized......this may at least give you High Speed fan working for better cooling!

    If High Speed running does not now happen then the Fan Motor must be bad.:(

    If you have those two wires that I mentioned disconnected you can try touching them one-at-a time to +12 volts to see if the fan runs at both speeds...should confirm if the Fan Motor is OK!

    Then if needed you can start fitting a Double-Pole Double-Throw switch via a fused +12 volts supply to swing between the two fans!

    With everything connected back to normal you can use your Wire Piece tool to measure the Ground Wires of the 2 relay coils..pin #85 on the Relays... relative to +12 volts as the PCM switches Ground onto the Relay coils.;)