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Thread: CJ-5 crankcase ventilation problem

  1. #1
    Junior Member
    Join Date
    Jan 2016

    CJ-5 crankcase ventilation problem

    Iseem to have a crankcase ventilation problem. Pressure builds up in the crankcase and oil is forced upward into the oil bath air cleaner until it fills uo and pours out. Has anyone heard of this and maybe have some suggestions.

  2. #2
    Super Moderator bmorgil's Avatar
    Join Date
    Dec 2018
    Northwestern Ohio
    Wow silvar51, that is a serious issue! I am assuming this is an F134. The only way for the oil to get into the air cleaner is via the breather tube from the engine oil fill/dipstick tube to the air filter. For this to happen either the crankcase is way overfilled, or the "blow by" of combustion is severe. The first problem would be simple. Drain out some oil, but if it is blow by it requires an engine tear-down and rebuild.

    If the oil level is correct start the motor and remove the fill cap. If there is air puffing out of the fill tube you have to tear it down and find out why. Start it up and try to hold your hand over the fill tube with the cap off. There should be very little "pressure" there if any at all. As an engine wears more and more combustion gasses leak past the rings. A compression test is in order here. That will tell you a lot about why, if there is pressure in the crankcase.
    Last edited by bmorgil; 08-30-2020 at 07:44 AM.

  3. #3
    Super Moderator gmwillys's Avatar
    Join Date
    Aug 2017
    Make sure the PCV, (positive crankcase valve) is not stuck closed. This should be on the intake, down stream of the carb. On the L heads it's on the driver's side directly below the carb. F134 guys, chime in to the exact location. Okimark, your rough idle may be linked to your valve being stuck open.

    Willys was one of the first to use a PCV because the alternative was to have the crankcase vent to the atmosphere through a "slobber" pipe that went down next to the block and was open at the bottom. This doesn't bode well if you wade across a creek, and the engine fills with water through the tube.

  4. #4
    Senior Member
    Join Date
    Nov 2019
    I have no PCV valve and mine has the draft tube that goes down from the exhaust valve cover. There is a place that looks like a hose would connect on the oil breather but it has been plugged.

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