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Overheating Issue

Discussion in 'Early CJ-5 and CJ-6 Tech' started by jeepstar, May 17, 2018.

  1. May 17, 2018
    jeepstar

    jeepstar Member

    Sheboygan
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    Jun 28, 2006
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    937
    I went out on the maiden voyage for the summer in my '70 cj5. About 70 miles round trip, country roads. I was almost home and the temp gauge shot up to hot.

    134 fhead.
    New radiator
    New water pump
    New thermostat

    Been running the "new" stuff 2 years, radiator over 5, so its not really new.

    Where can i begin, what should i do?
     
  2. May 17, 2018
    47v6

    47v6 junk wrecker! Sponsor

    Washington DC.
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    Go over all the basics. Coolant, belt, see if water in oil, oil in water, etc.. Did it overheat? Boil water out of the cap? If it did, check thermostat, if not check gauge and wiring.
     
  3. May 17, 2018
    jeepstar

    jeepstar Member

    Sheboygan
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    No water boiled out. Ill check the oil for water today after work
     
  4. May 17, 2018
    PeteL

    PeteL Member Sponsor

    Hills of NH
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    After 70 miles?

    Check the wiring to gauge and sender.
    Fanbelt?
    Thermostat?

    Worst case - head gasket putting a bubble into the coolant space.
     
  5. May 17, 2018
    jeepstar

    jeepstar Member

    Sheboygan
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    I put 2 in last year. Last thing i want is to do it again.
    Googleing led me to an article stating the lower hose may kink from getting hot and suction from the water pump
     
  6. May 17, 2018
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    There's supposed to be a spring in there to keep it from collapsing.

    IR thermometers are cheap & provide a sanity check in these situations.
     
    dozerjim likes this.
  7. May 17, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    If you don't find anything wrong you might suspect the temperature gauge itself. I prefer mechanical gauges myself.
     
  8. May 17, 2018
    jeepstar

    jeepstar Member

    Sheboygan
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    What should the external block temp be? Ill try this too
     
  9. May 17, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    It should be relatively close to the water temperature. When you say shot up, do you mean quickly as in seconds? Or over a couple of minutes time?
     
  10. May 17, 2018
    jeepstar

    jeepstar Member

    Sheboygan
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    My instrument cluster has a C and an H. I was not paying that close attention to say if it happened within a minute or two. But I did look when I got to my destination and I did look Midway on the way home. And it was fine next time I look down it was way on the h
     
  11. May 17, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    My first suspicion is the fan belt then. Have you got the right width belt and is it tight?
     
  12. May 17, 2018
    Focker

    Focker Ran when parked... Runs while moving. Staff Member Sponsor

    Tri-Cities WA
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    X2
     
  13. May 17, 2018
    NCRenII

    NCRenII yellow fever Sponsor

    Far Nor Cal
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    Is the f head sender located where it needs to be purged of air? I had a jeep that was showing 24o* in the winter on a long trip, opened the cap and could stick my finger in the water. After replacing thermostat gauge still showed high, I replaced sender gauge and gauge read correctly. Years later I put the sender in another jeep and the "bad" sender read correctly. I attributed it to excessive thread sealant. Might try loosening sender (and bushing if present) and re-tighten to establish a good ground. Twist the terminal nut a couple times too.
     
  14. May 17, 2018
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    In my experience the block is exactly the same temp as the coolant, if the thermostat is open the upper radiator hose & inlet tank will be as well. You can measure a large difference between the top & bottom of the radiator as the coolant flows through it.
     
    Glenn likes this.
  15. May 17, 2018
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    If it made it up to H without loosing coolant, definitely check the gauge before you get too concerned. A cheap mechanical temp/oil pressure gauge is almost a requirement in an old rig.
     
  16. May 17, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    That is good to know, I've never checked both the block and coolant itself but certainly expected them to be close if not the same.
     
  17. May 17, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    There is a big difference indeed!
     
  18. May 17, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    What pressure radiator cap do you have?
     
  19. May 17, 2018
    jeepstar

    jeepstar Member

    Sheboygan
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    7 or 13. Cant remember off the top of my head. I went thru 2 headgaskets, you guys said the cap should be rated at X so it pops before the headgasket
     
  20. May 17, 2018
    Daryl

    Daryl Sponsor Sponsor

    Bonney Lake, WA
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    Infared thermometer is really cheap at Harbor Freight. It is a really good tool to tell what is getting hot and where. Virtually every spot on the motor is a different temp depending on where the water jacket is. Using one has totally changed my thinking on cooling. I am also a big fan of having a very small hole in the thermostat of an F-head as they tend to hold air in bubbles worse then any other engine that I have ever worked on.
     
    Glenn likes this.

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