It's Happened Twice Now....

Discussion in '2005+ Mustang GT 4.6L Tech' started by 07 Boss, Aug 12, 2020.

  1. 07 Boss

    07 Boss Senior Member

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    A week or so back my car overheated as I pulled into my driveway. Water pump is pumping, fan is going. Weird shit. I cooled her back down and added water to the system and then could not duplicate it. Idled in the driveway for 30 min. with ac on. Turned ac off and ran a high idle for about two minutes to even get the temp up to normal. Been driving her daily all week 100*+ days with no issues. Happened again yesterday sitting at a light. Managed to get it into the gas station on the corner and shut the motor. Once she stopped spewing coolant I ran the pump and added water and cooled her back down in a couple of minutes. Sat there with the car running, nothing out of the ordinary.

    First thought is the thermostat which I will pull today or tomorrow but it strikes me as weird is you wouldn't think it would be this intermittent of an issue if the thermostat was sticking, no? Or can it just shut randomly? I mean car was up to temp and been driving about 20 minutes before she got hot.
     
  2. TylerM

    TylerM Member

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    Edit:

    Is the original radiator in the car?

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  3. MrBhp

    MrBhp Member

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    Mine was doing that. Turned out to be the "overheating in the fuse box" problem. Fan would only work properly when I was staring at it. Would run slow or not at all when I would turn my back. I tricked it with an elaborate mirror setup. I moved the relay, fuse, and feed wiring outside the fuse box.
     
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  4. DieHarder

    DieHarder Member

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    MrBhp - Senior citizens, although slow and dangerous behind the wheel, can still serve a purpose... Targets - DeathRace 2000
     
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  5. 07 Boss

    07 Boss Senior Member

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    Yes it's the original radiator. Cooling system gets flushed every other year.
     
  6. TylerM

    TylerM Member

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    Ok. I had a similar issue, the only thing that cured mine was replacing the radiator. I upgraded the water pump and radiator fan at the same time.



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  7. bl817

    bl817 Member

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    MrBhp, do you have a write up with photos on how you did that? I have a thread bookmarked from a while ago and all the pics are gone
     
  8. MrBhp

    MrBhp Member

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    I will see what I can find. Car is currently not at home. F'n transport.
     
  9. Wingrider

    Wingrider GT500 track guy

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    Big air bubble in the cooling system? I know often you need to put vacuum to the system to any air out of an trouble spots.
     
  10. bmeaggie

    bmeaggie Junior Member

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    I had this exact problem earlier this year. I tried every recommendation that I could find. I was changing coolant, squeezing tubing trying to get bubbles out. The problem started very intermittent and slowly became more frequent. I finally got the overheating to happen when I could pull over immediately and when I did the fan was stopped. Now of course everyone told me that fan failures were very rare, and that it must have been something else. I had a GT500 fan that was only 4 years old after all. The fan relays were crazy hot... melting when the failure would occur. Now people were telling me it was the fuse box, as if fuse boxes without extreme age or corrosion just “go bad.” I ordered a new GT500 fan from Summit, installed it and problem gone, and has stayed gone. The fan was drawing too much current, overheating the fuses and causing the system to shut down.
     
    Last edited: Aug 13, 2020
  11. 07 Boss

    07 Boss Senior Member

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    Interesting, I have a manual switch for my fan and pump that I can use if I need to but will look into the fuse box heat issue. I started the car this morning with no ac and drove all the way to work stopping for smokes. Got to work and the car was at it's normal temp but the fan wasn't on. I just now went to the store and back and started the car with the ac and the fan was running the whole time. I haven't been to the track in a while so I will have to put a new fuse in that circuit since I wasn't using it.

    [​IMG]


    How did you track or diagnose this fuse box issue? Everything seems to be OK when I look at it.
     
  12. 07 Boss

    07 Boss Senior Member

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    Well I'm not going to throw a bunch of parts at her and hope. The pump is new, the radiator is clean and flowing, and the fan works. I'm leaning to something electrical or ecu related.
     
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  13. 07 Boss

    07 Boss Senior Member

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    I have a tall crossover with a bleeder valve on it.

    [​IMG]
     
  14. 07 Boss

    07 Boss Senior Member

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    I'm going to look into this a bit more. I think I will wire an LED into the ground side of the fan motor so I can see when it turns on and off. At least then I can monitor it real time.
     
  15. Juice

    Juice forum member

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    You need to figure out if overheats and pushes coolant out

    OR

    You have a small coolant leak that causes the car to overheat because the coolant got low.
     
  16. bmeaggie

    bmeaggie Junior Member

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    Some more important points:

    I eventually realized that my fan would usually stop working on the second leg of my errand... meaning I would take one of my 10,000 children to soccer or something, and everything would be fine on the way there. Then, on the way home the AC would start blowing hot air and the temp would suddenly start climbing. It would climb fast too.

    I think the fan motor was dying, drawing too much from the relays, and the relays would eventually overheat/expand/whatever and stop working. Then the fan couldn’t turn on anymore, but after cooling down the relays would work again.

    So... key things with my failure mode were 1) car had to heat up first... would never happen on cold startup 2) AC would start blowing warm air 3) the fan relays would be crazy hot to the touch when fan wasn’t coming on.

    Good luck! Curious what your root-cause turns out to be. Let us know and how you fixed it please!
     
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  17. 07 Boss

    07 Boss Senior Member

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    Well from what it looks like is the fan runs all the time when the ac is on as expected. It's when I turn the ac off does it seem to have issues. The signal to the fan goes through the same relay whether its the ecu or the ac telling it to go on right? I haven't pulled the fuse box apart yet but I will at least throw the horn relay in the fan relay spot and see if the thing comes on.
     
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  18. Juice

    Juice forum member

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    Ecu turns on the fan. For AC or for coolant temp.
     
  19. bmeaggie

    bmeaggie Junior Member

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    So to make sure... have you overheated the car, opened the hood without shutting off the engine, and made sure you can still activate the fan by turning on the AC?

    If “yes” to that for certain... There are TWO fan relays... a high speed and a low speed (1 & 2). I think the high speed = ac activated. Maybe your low speed relay is bad?
     
  20. Juice

    Juice forum member

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    Good point about the 2 relays.
     
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