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Thread: "?blowby?" problem-258 motor

  1. #1
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    Default "?blowby?" problem-258 motor

    Well, in my CJ sits a pretty good 258, I've replaced the transmission, exhaust, carb and generally babied it where the previous owner just pounded and parked it for years....but I'm still chasing an oil leak problem:
    Upon startup (and even when warm), she doesn't have any abnormal blowby from the valve cover....but after driving to/from base, I get oil leaking from the crankcase breather. I replaced the PCV valve/breather and even swapped the locations between the two....it only changed the location where the oil was seeping.....

    I'm moving ahead with two PCV valves today and will repost if this fixes or at least slows the problem. Wish me luck, would ya?
    83 CJ-7, 4"lift, 258/T-4/D300/3.73 33" ProComp ATs
    To do list: finish roll cage, paint, front/rear bumper set up.

    "Make no mistake, choosing the lesser of two evils is still choosing evil"--J Garcia

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    .JOATMON devildog4x4's Avatar
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    Two PCV's won't get it. You need one and a line to your air filter.
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    youre prolly gonna need rings or valve seals. theres way to bandaid the problem like routing the pcv to the air cleaner, putting a blow by catch can on it, but there will still be the issue with blow by.

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    Senior Member HillBillE's Avatar
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    Quote Originally Posted by 91YEEPER View Post
    youre prolly gonna need rings or valve seals. theres way to bandaid the problem like routing the pcv to the air cleaner, putting a blow by catch can on it, but there will still be the issue with blow by.
    What he said!

    Unfortunatly, the 258's are known for blowby when they get some miles on them.

    It's more than likely a combo of worn rings and valve guides.

    I actually removed my line to the air cleaner, and replaced it with a small filter, but left the PCV valve/hose to the carb.

    I had used a vented 'catch jug' for a while also, but it got to where there would be a quart+ of oil after a 70 mile run


    When you first start it, the oil is still 'thick', and everything is cool, so the blowby isn't as bad. Once the engine warms up, it'll get worse.


    I used some of the "Lucas Oil Treatment" in my old 258, and it helped some, got me by for a few months until I could rebuild the motor.

    If there is a lot of blue smoke coming from the exhuast, it means the rings are shot.

    If not, the valve guides are shot.

    Even on my fresh rebuilt 258, with under 10K miles on it, I had a small amount of blowby. Mainly becuase of the RPM's at highway speed.

    Around town, It went through no oil, but on the freeway it would tach around 3400 RPM's to hold 75 MPH, and it would loose some oil.

    Not bad, only used 2 quarts in the 1500 mile trip to Moab

    But even fresh, the 258 shouldn't he tached up more than 4000- 4200 RPMs for very long.


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    Administrator korisu56's Avatar
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    Yeah, i remember my problem was worst when I put the engine under load. Would get so bad I would be embarrassed at lights.

    Good luck though bud

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    darwinism at its best irish1371's Avatar
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    stock vavle cover? after markets maybe missing oil shield making your problem worse
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    Yeah, I tried the "to the aircleaner" bit, but it just sucked the oil into the carb base plate (then down the intake/block/ground)....I'm agreed that the valve seals are most likely the problem, there's no smoking going on.

    I did drive it today to Bragg and back----zero oil lost and no smoking. It might be a band aid for now, but it's working today and the parking spot doesn't look like the Valdez. I'll start saving/planning for a valve job soon--I drive it about 80 miles a day, can't be long before this patch wears out. I'll keep ya'll posted on it. And thanks to all for the inputs!
    83 CJ-7, 4"lift, 258/T-4/D300/3.73 33" ProComp ATs
    To do list: finish roll cage, paint, front/rear bumper set up.

    "Make no mistake, choosing the lesser of two evils is still choosing evil"--J Garcia

  10. #10
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    Another 80 miles with zero oil lost. Fingers still crossed, but happier than last week!
    83 CJ-7, 4"lift, 258/T-4/D300/3.73 33" ProComp ATs
    To do list: finish roll cage, paint, front/rear bumper set up.

    "Make no mistake, choosing the lesser of two evils is still choosing evil"--J Garcia

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