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Engine overheating only over 40mph (was:willys cj5)

Discussion in 'Early CJ5 and CJ6 Tech' started by kundert, Aug 20, 2007.

  1. Aug 20, 2007
    kundert

    kundert New Member

    Joined:
    Oct 4, 2006
    Messages:
    5
    what makes engine overheat after flushing system, replacing head gasket, installing a new thermostat?When remove thermostat temperature remains fine. Is it alright to run without thermostat installed? :?
     
    kundert, Aug 20, 2007
    #1
  2. Aug 20, 2007
    Txjake

    Txjake I wrenched with Sparky

    Oklahoma City OK
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    Feb 3, 2006
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    544
    Re: willys cj5

    have you tested the radiator cap? pressur tested the rad?
     
    Txjake, Aug 20, 2007
    #2
  3. Aug 20, 2007
    mb82

    mb82 I feel great!

    Charlottesville Va
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    Mar 17, 2003
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    2,706
    Re: willys cj5

    a bad new themostat. Or an airbubble in the system being caught by the thermostart
     
    mb82, Aug 20, 2007
    #3
  4. Aug 20, 2007
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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    Re: willys cj5

    This has come up before, somewheres or another.

    Do you have a heater?

    If so, is the valve open to allow circulation through the core?

    If you do not have a heater, is there :

    a) A bypass hose from the water pump to the front of the head?

    or

    b) A hose connecting the heater hose outlet on the water pump to the coolant port on the rear top passenger side of the head?

    If you don't have these either add one or try drilling a 1/8" hole in the thermostat diaphram to prevent an air/steam bubble building up underneath it.
     
    Howard Eisenhauer, Aug 20, 2007
    #4
  5. Aug 20, 2007
    lamar

    lamar Member

    greenville sc
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    Jan 25, 2004
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    Re: willys cj5

    are you installing the thermostat correctly? if you put it in backwards it will overheat.
     
    lamar, Aug 20, 2007
    #5
  6. Aug 20, 2007
    kiowamtp

    kiowamtp Member

    DFW
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    Re: willys cj5

    :iagree:
    Beat me to it.
     
    kiowamtp, Aug 20, 2007
    #6
  7. Aug 20, 2007
    kundert

    kundert New Member

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    Oct 4, 2006
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    Re: willys cj5

    I have checked all that out, still have the problem.
     
    kundert, Aug 20, 2007
    #7
  8. Aug 20, 2007
    kiowamtp

    kiowamtp Member

    DFW
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    Re: willys cj5

    How about putting it in a pot of water and watching it "open" to ensure it does work right? I had a bad "new" thermostat once that I wasted copious amounts of money trying to troubleshoot.
     
    kiowamtp, Aug 20, 2007
    #8
  9. Aug 21, 2007
    kundert

    kundert New Member

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    Re: willys cj5

    It only over heats when I go over 40 mph, if I stay under that it is just fine. So last nite I replaced the radiator with an differt one I had here, I hope that will solve my problem or otherwise I am back where I started. help
     
    kundert, Aug 21, 2007
    #9
  10. Aug 21, 2007
    BlueFlu

    BlueFlu past owner of some ecj5's

    Hermitage, TN
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    Jan 21, 2004
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    What kind of fan do you have on it?
    Does it have a fan shroud?
     
    BlueFlu, Aug 21, 2007
    #10
  11. Aug 21, 2007
    kiowamtp

    kiowamtp Member

    DFW
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    Fill out your profile there maybe someone nearby. Also, what engine you running?

    As far as the f-head goes, when I first got my JEEP together and running I had a similar problem. The PO never installed the bypass hose and I would overheat over 40. But I never kept it running long enough at idle to see if it would do it then. Here is a pic of the bypass hose.
    [​IMG]

    Also, if your timing is off it may cause you to overheat.
     
    Last edited: Aug 21, 2007
    kiowamtp, Aug 21, 2007
    #11
  12. Aug 21, 2007
    Tall Grille

    Tall Grille New Member

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    Aug 19, 2007
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    Drill a 1/8" Hole through the sheet metal disc of the thermostat. This will aloow air bubbles to pass through the 'Stat it will also allow a constant small flow of coolant through the system.
     
    Tall Grille, Aug 21, 2007
    #12
  13. Aug 22, 2007
    lynn

    lynn Time machine / Early CJ5 HR Rep Staff Member

    Huntingdon PA
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    Sep 20, 2002
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    Keven, I'll bet that's why my '48 used to overheat... it didn't have a bypass hose like that... :rofl:
     
    lynn, Aug 22, 2007
    #13
  14. Aug 23, 2007
    StraightToPlaid

    StraightToPlaid Ludicrous speed!!!!

    West Chester, OH
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    I was "overheating" for a bit and it was driving me crazy. The thing was that it really didn't feel that hot inside inside the engine compartment. I started thinking it was heating up WAY too fast (said it overheat in maybe 2 or 3 minutes), it was running much better then an engine that hot should have, and it just didn't feel hot.

    It turns out my gauge was bad, it was over reporting the temperature. If you've done all that maybe you just want to try a new gauge, they're cheap and you'll be kicking yourself if that's what the problem is.
     
    StraightToPlaid, Aug 23, 2007
    #14
  15. Aug 24, 2007
    kundert

    kundert New Member

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    Willys CJ5, I replaced the radiator now everything works just fine, I was lucky that I had another one here to replace it with. Thanks for all the help.
     
    kundert, Aug 24, 2007
    #15
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