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Boiling Gas And Vapor Lock - Just Started Happening

Discussion in 'Early CJ5 and CJ6 Tech' started by 60CJ5, Nov 20, 2019.

  1. Nov 22, 2019
    Norcal69

    Norcal69 Out of the box thinker 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Northern California
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    Have you tried slicing a length of Rubber hose open and putting it over your hard fuel line?
    Can you install a clear fuel filter right before the carb to verify fuel availability when it wont start hot?
     
  2. Nov 22, 2019
    Boyink

    Boyink Super Moderator Staff Member

    Tulsa, OK
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    Sep 20, 2002
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    I recognize that rig...

    Another Tellico veteran...;)

    How ya been?
     
  3. Nov 22, 2019
    wasillashack

    wasillashack Member

    Wasilla, Alaska
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    Mar 17, 2008
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    OK, let's go back to physic class. Vapor lock is when a pump cavitates and the gases separate from the liquid, either from inadequate supply or the pump losing efficiency (pressure) due to mechanical wear or valve malfunction, cavitation will destroy many pumps, especially centrifugal pumps, if not eliminated. The cavitation sound you hear is the gas bubbles colliding with the pump volute (bowl) which will actually make the surface of wear rings and volutes look pitted, which it is. As I said,. it is very destructive. If your fuel was really boiling you most likely wouldn't be posting here, look up BLEVE.
    Back in the flathead Ford days, they were notorious for vapor locking due to poor location of the fuel pump, poor fuel pump design and flatheads' tendency to overheat. The common cure was to clamp 3 or 4 clothes pins on the fuel line between the fuel pump and carburetor, this acted as a heat sink this allowed the gas bubbles to be re-absorbed and rich folks would wrap the fuel line with aluminum foil before installing clothes pins. Reducing the liquids' temperature reduces the tendency to boil. Pressurizing any liquid raises its' boiling point----think radiator and pressure cap. Weak pump=cavitation. I'd check the supply line first to see if the pump is getting adequate supply. Good luck!
     
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  4. Nov 22, 2019
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    I run a stock '34 flathead Ford V8. In twenty-plus years it has never vapor locked, or overheated. The fuel pump design is not fundamentally different from many other vehicles, including the F-head. They all have a spring-driven rubber diaphragm and I seriously doubt that they are capable of actual cavitation, which is the instantaneous and energetic collapse of bubbles.

    When they did vapor-lock it was because the fuel pump sat on top of the hot engine, and had a very long suction-side draw from the fuel tank. Under suction and excessive heat conditions, the gasoline could form vapor on the intake side, reducing the pump's ability to draw liquid fuel. Installing a heat sink on the carb side makes no sense to me because that is the output (pressure) side.

    Some present-day Flathead Ford owners use an in-tank pump to pressurize the entire fuel line.

    The F-head has a similar suction-side supply line from the tank, but is much shorter. I agree that he should check for adequate supply, and also any abnormal heating from the exhaust pipe. If I were him I'd also check that the gas cap is venting well.
     
    Last edited: Nov 22, 2019
    Jrobz23, 45es and ITLKSEZ like this.
  5. Nov 22, 2019
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    I almost suggested this as a last resort.

    The Volvo fuel system I’m working on has a low-pressure in-tank pump to feed the under-car high-pressure pump. This was absent in the earlier models and was added in the late 70s(?) to aid against reports of vapor lock.

    Higher pressure raises the boiling point, pressure lower than atmospheric levels lowers the boiling point.
     
  6. Nov 22, 2019
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    Yes, but millions of F-heads have had no problem for decades. There is a fixable problem, not a design flaw.
     
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  7. Nov 22, 2019
    45es

    45es Active Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Naches, WA
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    The OP stated he has had the Jeep for years and has not had any fuel problems until recently. I suggest he follow the above advise.
     
  8. Nov 22, 2019
    60CJ5

    60CJ5 Member

    Alabama
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    Boyink, doing well. Jeep has been a nice day driver for years as the kids grew up. I always considered it very reliable until this started happening. Tellico was a blast and wish I could find some more event like that one. Most the time it seems like they are out west or just too far.

    Have to get this figured out. Who is the best supplier of fuel pumps for F134s out there? I would rather pay a little more for quality if it is available. I am also going to move / insulate the fuel line where it runs near the exhaust. maybe that will fix the issue and I can trust the ol girl once again.

    thanks for the comments on the Jeep. I do love driving it but man I was close to giving it up this summer. As I said in a post on here a long time ago, it seem like if you beat the heck out of these things they will just keep running to spite you but if you take care of them there is always something to fix. Not fair!!! there are advantages and comforts to riding in my daughters JK or my sons JL...…
     
  9. Nov 22, 2019
    60CJ5

    60CJ5 Member

    Alabama
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    Jan 29, 2003
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    PS the gas cap vents TOO much, the cork seal is about worn out :D
     
  10. Nov 23, 2019
    Wayngro

    Wayngro New Member

    Central WA. state
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    NOOOOOO! Don't do it! You'll regret it for the rest of your life. Ask me how I know.
    Anyway, after not reading past your post above, I'd say your fuel isn't boiling in the tank but in the fuel bowl of the carb.. Is the isolator spacer still between the two gaskets under the carb.? If not, you need to put one back in. A Phenolic one is what you want iirc.
    This being said, I've been wrong before and am in no way any kind of mechanic that anyone should take advice from.
     
    65CJ5 SRD likes this.
  11. Nov 23, 2019
    wasillashack

    wasillashack Member

    Wasilla, Alaska
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    Sorry to all to all for not being more specific in my earlier post. I meant to say cavitation is the sound of the gas bubbles collapsing when they collide with the volute or other internal pump parts. And I thought I was pretty clear about restricting my comments to flathead Fords, apparently some took my comments to include F head Jeeps, too many F's can be confusing.
     
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  12. Nov 23, 2019
    Wayngro

    Wayngro New Member

    Central WA. state
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    My Jeep had an air leak at the outlet on the tank. It was a badly cracked fuel hose. It was sipping air and not getting enough fuel to the carb..
     
  13. Nov 23, 2019
    wasillashack

    wasillashack Member

    Wasilla, Alaska
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    Had the same issue on a '67 Chevelle SS, crack in the fuel l just above a rear tire, intermittent, stalling, hard to start, drove me nuts until I put some pressure on the gas tank, less than 5 PSI, and had someone listen for an air leak. Good luck!
     
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  14. Nov 25, 2019
    60CJ5

    60CJ5 Member

    Alabama
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    cold starting is not a problem. it has been sitting for 3-4 months untouched and started on the 3rd or 4th crank yesterday. I didn't get a chance to look at anything, I had to move it so I could clean up around it as the wife wants the Christmas boxes out of the attic this week. A sitting car becomes a storage shelf pretty quick around here. I took it out for a short run around the neighborhood and it ran like a champ but it hardly got up to temp. the only thing acting up was the AMP light was on most of the time but I "think" that was just a low battery and a generator working to charge it. AMP light went out when I pulled back in driveway (4-5 minutes of driving)
     
  15. Nov 25, 2019
    zila

    zila I throw poop

    Rock Springs,...
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    X2. If you are hearing noises in the tank I am thinking venting.
     
  16. Jun 13, 2020
    66cj5

    66cj5 Jeep with no name

    NorthWest Indiana
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    It sounds like the cap isn't venting and causing a vacuum in the tank (hence the air bubble sound). Try loosening the cap slightly and see if it solves the problem.
     
  17. Jun 13, 2020
    Jonbbrew

    Jonbbrew Member

    Paso Robles, CA
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    WOW! A beauty! Great paint and color too! Yes, windshield rocks! :clap::clap::clap: Would love to see the motor too since the outside is so great!
     
  18. Jun 15, 2020
    John Gedde

    John Gedde Been around the block once or twice...

    Middle Island, NY
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    Someone with some wicked fabrication kills could make a bundle making a kit to retrofit to the split/ventilated glass...

    John
     
  19. Jun 15, 2020
    Michael Wedin

    Michael Wedin Member

    Sweetwater, TX
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    Mar 20, 2020
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    One simple way to verify hot gas lines or cracked fitting or hot tank is to run a separate gas hose on the outside of jeep from the fuel pump and stick it down into tank and run it. If everything goes away, then work backwards from fuel pump. I've had the same problem and had to replace the gas line . It would suck gas from tank and , through a leaking or cracked fitting, a small amount of air would enter due to the sucking action of fuel pump, and then finally carburetor would run out of fuel. As others mentioned, evaluate the check valves in the fuel pump for scoring . Put your detective hat on and rule out one little thing at a time.
     
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