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V6 Still Overheating!

Discussion in 'Early CJ5 and CJ6 Tech' started by Buildflycrash, May 28, 2019.

  1. May 28, 2019
    Chilly

    Chilly Active Member 2019 Sponsor

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    About overheating because water isnt spending enough time in the radiator to transfer the heat. I've heard that several times so it's understandable that this theory never dies. It's just contrary to physics and thermodynamics is the problem. If it were true then the high flow rate would also prevent the coolant from picking up heat from cylinder walls. Removing thw thermostat isnt a good idea, but its not because the radiator needs more time to hand off thw heat.
     
  2. May 28, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    This is what I have heard too. Normally no thermostat can keep an engine from getting up to proper operating temperature in colder weather, so it seems that should hold true for warmer weather also.
     
  3. May 28, 2019
    NCRenII

    NCRenII yellow fever

    Far Nor Cal
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    Have you noticed normal operating temps at around town, lower rpm and increased temps at highway speeds? Perhaps the the lower hose is collapsing?
    To check get the engine and coolant warm and circulating. Do this by removing cap starting cold engine and let it idle until you notice the coolant circulating. When that happens, replace cap securely and have an assistant increase rpm up into the higher limit and watch the lower hose to see if it collapses. If so you probably need a spring inside the lower hose, or a new flex hose that does not need a spring.
     
  4. May 28, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

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    You'd think so but I've seen it happen on engines running without a 'stat. put it back in & all is oakey doakey.
     
    jpflat2a, RATTYFLATTY, Glenn and 2 others like this.
  5. May 28, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member

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    Certain types of engines or certain design?
     
  6. May 28, 2019
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

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    Thanks for all the input. First order is putting the thermostat back in. Second is finishing installation of shroud. The gauge is brand new and I really do think it is correct. Puzzled because this happened at 50mph and obviously had plenty of air flow.

    I’ll check the lower hose as someone suggested. It doesn’t have a spring inside but it is new.

    About the heater hose in the first photo- is that even necessary? It is a little flattened out, not kinked but I see heaters with valves completely cutting out the flow through this part of the system??
     
  7. May 28, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member

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    I don't think it's necessary since it doesn't do anything. I am wondering though if it is possibly causing a turbulent flow because of the kink? Could that possibly be affecting the temp. sending unit reading?
     
  8. May 28, 2019
    Oldriginal86

    Oldriginal86 Member

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    Or is the hose just letting the water pump suck in the hot water from the intake manifold and not the cooled water from the radiator. I would pinch off that hose and run it again.
     
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  9. May 28, 2019
    Focker

    Focker That's what I do, I know things and I fix stuff. Staff Member 2019 Sponsor

    Tri-Cities WA
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    NIB doesn't always mean it works. Process of elimination. If not the gauge, maybe the sender? I'm only suggesting since you're not boiling over.
     
  10. May 28, 2019
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

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    Sender came new with the gauge. I’ll keep both on the list of possible failure points.
     
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  11. May 29, 2019
    Chilly

    Chilly Active Member 2019 Sponsor

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    I think the mechanism that leads to overheating without a t-stat is pump cavitation from low head pressure.

    What happens when flow is increased is a reduced temp difference between hot side and cold side. Reduced flow increases rhe differential. Overheating happens when the water around the heads gets hot enough to boil, even though the radiator outlet may be nicely cooled from loitering in there a good long time.

    Another thing about coolant flow: the water pump flow doesnt actually aid cooling at all except so far as to keep things moving well enough to prevent localized boiling at hot spots. Its the AIR that takes the heat away. The water simply carries the heat to where the air can get to it. One cant "water pump" their way out of an overheating problem. Either the combustion events are putting too much heat in, or the radiator isnt getting enough out. Water is simply the messenger
     
  12. May 29, 2019
    Chilly

    Chilly Active Member 2019 Sponsor

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    Tell me about your engine. Is it rebuilt? Did you raise compression? Change cam? You've replaced a bunch of things in cooling system so I'm not concerned for that. Except to install thermostat and check for collapsing lower hose as recommended already. I'm also of the camp that thinks shroud isnt very important at highway speeds, though I am a proponent of using a shroud.

    If you raised CR and/or raised cylinder pressure with a cam designed for low end grunt (early closing intake) then your engine will want more advance. Running high octane fuel will also warrant a smidge more advance since it burns a little slower than low octane fuel (unnecessary without higher cyl pressure though).

    After checking some easy stuff maybe throw another couple degrees of advance and see what happens.
     
    Last edited: May 29, 2019
  13. May 29, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

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    Specifically it was an ancient Lister diesel used on a genset.
     
  14. May 29, 2019
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

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    Reinstalled the thermostat and clamped off the heater hose this morning...

    [​IMG]

    Heading to NAPA at lunch to get a spring for the lower hose (I think this is the problem/solution).

    [​IMG]
     
  15. May 29, 2019
    NCRenII

    NCRenII yellow fever

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    I'd recommend un-clamp the heater loop hose.
     
  16. May 29, 2019
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

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    That's an easy one to undo for sure. Can you give any insight to the function of the hose? How about folks who have valves on heating systems to shut down in summer? Thanks for the reply
     
  17. May 29, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

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    A few more thoughts on the not 'stat/overheating controversy.

    It occurs to me that there may be another explanation other than the coolant not spending long enough in the rad to loose heat argument.

    Consider that there are actually two circuits for coolant to follow in/out of the pump- one through the block and one through the radiator. The flows come together & diverge at the pump where, ideally, they will mix in a proportion that will ensure an adequate amount of coolant from the rad will end up going into the block (usually actually the head(s)) & likewise an suitable amount of heated coolant from the block will end up going towards the radiator. Inherent in this design is that the flows through the rad & the engine will be somewhat balanced, balance will depend on the restriction/resistance to flow being somewhat the same between both circuits.

    Now, remove the thermostat from the radiator circuit, what happens?

    The probable outcome is that the resistance to flow through the radiator circuit drops- depending on the specifics of the engine, pump & radiator perhaps by a fair percentage. All other things being equal I would expect the flows to become unbalanced now favouring the rad, i.e. more coolant through the rad & less through the engine. With less coolant flow through the engine it's temperature will of course rise, conversely with less coolant from the block going into the pump there's less mixing with the rad coolant.

    And of course if the rad circuit is flowing faster we're back to the theory about the coolant not having enough time to cool off enough compounding the issue.

    Again this would be dependent on the design of the engine cooling system & impacted by non-stock components but in my experience with systems apparently small differences can have major impacts on performance explaining why the issue seems to affect some vehicles but not others.



    Counterpoint anyone?
     
  18. May 29, 2019
    Chilly

    Chilly Active Member 2019 Sponsor

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    Howard, that makes sense. Cant believe I wasnt thinking of the flow back into the block, I suppose because the hose to radiator is so much more obvious. Balancing the flow makes perfect sense, and effect of unimpeded flow to the radiator path should have a causal effect of reduced block flow to the point of boiling. Radiator circuit would be cooling like crazy but the block is growing ever hotter. You're a smart guy!
     
  19. May 29, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

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    Yeah I had to think about it a bit :confused:- what you posted earlier is perfectly expected behavior from the simple heat generation/heat transport/heat exchange view of things, gave me a bit of a queezy puzzled cognitive dissonance feeling :ill:

    There's no guarantee I'm correct on this but it is a possible way out of the quandary- there's , besides my own, lots of examples out there of this being an observed phenominainia.

    Interestingly all the diagrams I can find on the net do not show the "separate circuits" thing happening, they all show nice cool water from the rad going into the block & only the block and the hot coolant going to the rad & only the rad.:shrug:
     
  20. May 29, 2019
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

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    No spring at NAPA so I'll try just the thermostat install and let you know tonight.
     

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