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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 20, 2019
    60CJ5

    60CJ5 Member

    Alabama
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    Jan 29, 2003
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    162
    I have had my Jeep for 20+ years and have never noticed gas boiling in the tank until the last year and it has started acting up (dies) when it is really hot. In chasing this I have replaced all the fuel lines (fuel pump to carb. didn't replace the tank to fuel pump because the tank was full and I really didn't want to get soaked in gas) and put a good carb on it. I have not replaced the fuel pump - I think it is pumping fine.

    After being towed home 2 times this summer, I parked it and have not looked at it. but I am now done being mad at it and need to fix the issue.

    it is a "stock" 60 cj5 so there is no return fuel line.

    Am I correct in assuming that the gas boiling in the tank is a good sign that my issue is truly a vapor lock? not sure why it would have just started happening in the last year. I had not done anything prior to starting.....

    if that is the "issue" are there any known fixes?

    PS the exhaust system was replaced when I rebuilt the Jeep 20 years ago and is still solid (no rust out)
     
  2. Nov 20, 2019
    65CJ5 SRD

    65CJ5 SRD Member

    NM
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    Aug 12, 2019
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    101
    Lots of others here have more knowledge with this than me, but one thing to check your cooling system in case the engine is getting too hot (and heating up the carb which is then boiling the fuel). Check that fuel lines are not too close to heat sources. If you have some near heat sources you can try wrapping the lines with stuff from the parts stores sold for this purpose.

    Also see if you can remember doing anything to the Jeep or anything that happened at the time that might have precipitated the trouble. Always look at the last thing you worked on!
     
  3. Nov 20, 2019
    60CJ5

    60CJ5 Member

    Alabama
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    Jan 29, 2003
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    don't recall doing anything to it prior to the issue starting. Now that I "think" about it, I did have to rehang the tailpipe. Wonder if I moved it just enough to start causing the issue???? have to go look at that....
     
  4. Nov 20, 2019
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    You’re certain the gas is boiling in the tank?
    You’re certain this is a fuel issue? How?

    Modern fuels don’t boil until the 185° range. Ethanol fuels will boil at lower temps, but not much. If you truly do have an issue where your fuel is reaching those temps in the tank, fix it. That’s not good.

    Did you do an electrical tuneup around the time of the symptoms starting? I ask because it sounds a lot like a “new” condenser. It seems that the industry has forgotten how to make them, and it’s nearly impossible to get a good one.
     
  5. Nov 20, 2019
    60CJ5

    60CJ5 Member

    Alabama
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    this summer I was so sick of chasing this issue, I almost sold the thing! Had a For Sale post written up and then chickened out before I hit post.
     
  6. Nov 20, 2019
    60CJ5

    60CJ5 Member

    Alabama
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    I can hear it boiling in the tank when I turn the Jeep off.
     
  7. Nov 20, 2019
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    I’d start by inspecting the entire length of the fuel line, and make sure it’s far enough away from any heat sources, or has heat shielding between. It’s just going to take some good-ole investigative work to find the culprit. Something is causing the fuel to overheat. My guess is, it’s heating in the line somewhere, vaporizing, and what you’re hearing is bubbles being blown up from the bottom of the tank like a straw in a glass.
     
  8. Nov 20, 2019
    PeteL

    PeteL Member 2020 Sponsor 2019 Sponsor

    Hills of NH
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    I think you need to separate the issues, and examine them without making assumptions. True vapor lock is not usual in these Jeeps

    - You are hearing a noise in the tank - but you don't know if it is actually "boiling."

    - The engine dies when "it is hot." What is hot? The weather, the engine, the fuel, the street? Hard fast running or idling in a traffic jam? Are you sure the line to the tank is not clogged?

    - You "think" the fuel pump is fine. What reason do you have to assume that? It needs to provide both volume and pressure. A leaky diaphragm can connect the fuel side to the crankcase.


    I think ITLKSEZ has a good angle on this. If you have the stock under-seat tank, it runs quite close to the exhaust. It is only four feet of line to check, move, or replace. Standard 1/4" brake line and fittings
     
    Last edited: Nov 20, 2019
    ITLKSEZ likes this.
  9. Nov 20, 2019
    baldjosh

    baldjosh Sponsor

    pacific north west
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    is the tank hot to the touch??? not just near the exhaust but everywhere...if its boiling fuel then the tank should be HOT allover
     
  10. Nov 20, 2019
    60CJ5

    60CJ5 Member

    Alabama
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    never thought to check the temp of the tank..... it runs great until it gets up to temp then it will start dying most of the time it will restart but had a couple times this summer (90+ alabama heat) that it was dead. Don't drive it in the winter as it has not top or heat.

    going to check the spacing on the fuel and exhaust lines. I may have moved the exhaust when I rehung the tailpipe. it seems like I did that before these issues started.

    been a long yr with the ol Jeep worn out key broke off in the ignition and had to hot wire it to get home. then the temp gauge acted up (the needle was stuck) then this started...…. upload.jpg

    I was really close to selling it and buying a JL but the kids love the ol Jeep.
     
    Walt Couch likes this.
  11. Nov 20, 2019
    Twin2

    Twin2 not him 2020 Sponsor 2019 Sponsor

    Virginia Beach, VA
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    wow
    that's a pretty jeep
    I think the guys are on to something
    I don't think gas in tank is boiling
    just whats in line and burbling when it gets hot
    pete has a good point . if the diaphragm is leaking . could cause pressure from crankcase to push the fuel back


    on second thought . yea you need to sell it :D
     
    47v6 and ITLKSEZ like this.
  12. Nov 20, 2019
    liquids

    liquids Old Member 2019 Sponsor

    Detroit-ish
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    The gas tank is right under your seat. If it were hot enough to boil, your *** would feel it. It's not boiling there. Whatever you're hearing is something else. Gurgling in the line as fuel returns to the tank from a line where it actually did boil?
    Which engine? On my V6 the pump is right next to the left exhaust manifold with a heat shield between them.

    And yes, damn fine looking Jeep!
     
  13. Nov 20, 2019
    baldjosh

    baldjosh Sponsor

    pacific north west
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    X3
    I was just thinking about this
    same thought occurred to me...don't give up on the old girl...you'll get it figured out
     
  14. Nov 20, 2019
    PeteL

    PeteL Member 2020 Sponsor 2019 Sponsor

    Hills of NH
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    Wicked nice windshield.
     
  15. Nov 20, 2019
    Cowboyjeeper

    Cowboyjeeper Member

    Show low az
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    A windshield like that is on my wishlist
     
  16. Nov 20, 2019
    givemethewillys

    givemethewillys Sponsor

    New Kent, VA
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    I just read through this thread, and my first thought is that you have a leak somewhere that is causing the fuel line to lose prime, and the "boiling" you're hearing is the fuel back flowing back to the tank. Can a hole in the fuel pump do this (I honestly don't know)?

    My guess is that you have a fuel pump problem, and don't have a vapor lock problem at all. When it gets hot, things expand and suddenly your pump loses its prime, the jeep stalls, fuel gurgles back to the tank.

    Wicked nice jeep by the way. Figure out the problem and continue to enjoy it for years to come.
     
    65CJ5 SRD likes this.
  17. Nov 21, 2019
    Keys5a

    Keys5a Sponsor

    Florida Keys
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    I am pretty sure you have a fuel pump issue. Most mechanical fuel pumps have two (or more) check valves in them, which activate independently of each other. If one valve malfunctions, it can allow fuel backflow to the fuel tank, causing the gurgling (boiling sound). If a check valve malfunctions, the pump may not pump effectively, if at all. This would also answer your "vapor lock" issue, which is not vapor lock, but a loss of fuel pressure from the pump not pumping effectively.
    I would be looking hard at the fuel pump as the source of your problems.
    -Donny
     
    Last edited: Nov 22, 2019
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  18. Nov 21, 2019
    Tom_Hartz

    Tom_Hartz Member 2020 Sponsor 2019 Sponsor

    North Carolina
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    I have been dealing with the same thing. I came up with heat and I think different fuel. I moved to NC from CA in 2015 and never had fuel boiling in the under the seat tank until we moved. My CJ has an electric pump pushing and no mechanical pump. I do have an fuel pressure gauge, headers and the mufflers under the doors outside the frame. I have insulated the mufflers along with ceramic coating the exhaust system. I could still hear it boil and when it did my fuel pressure would drop. What has seemed to do the trick was to design a fuel system with a return line back to the tank so now the fuel is always moving. She seems happy now.
     
    65CJ5 SRD likes this.
  19. Nov 21, 2019
    Alan28

    Alan28 Well-Known Member 2020 Sponsor 2019 Sponsor

    Châtillon en...
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    Very nice Jeep. It should be cleared with a good logic action and some money.
    You can check temp easily with a infrared thermometer it is a sort of pistol.
    Then you change or repair the fuel pump. You clean again the carb.
    Check temp of water when hot. No mystery. Need time.
     
  20. Nov 22, 2019
    Rick Whitson

    Rick Whitson Detroit Area 2020 Sponsor 2019 Sponsor

    I live South of...
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    I have a hard time with gas boiling in the tank, I agree with the theory of bubbling in the tank, the fuel pump must be the problem. If my gas tank was boiling I would not want to see what was going to happen next, I would be a long way away from it. Good Luck.
     

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