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Rattle coming from motor at idle only


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  • Rattle coming from motor at idle only

    I had this problem before the lift, Nth degree skids, and new driveshaft went in, but it was transient and hard to reproduce. Now, it happens consistently as follows:[list=1][*]Sounds like a metallic clanking that is around 3-4 times per second.[*]It seems to originate from the oil pan area.[*]It only occurs at low idle. Any application of the gas in any gear makes it disappear.[*]Oddly, it only occurs after the motor warms up after a few minutes. It seems less prominent if the car is on an incline when idling.[/list=1]

    There is a 1.25" body lift, but there doesn't appear to be any rub on the headers and steering or any other motor-mounted interference with tub-mounted objects.

    The engine skid mounts up directly to the engine and the transmission. There appears to be enough clearance between the skid and the headers. It's hard to tell by looking if there is any touching between the skid and the oilpan.

    There is no unusual fluctuation in oil pressure. I had given the oilpan a fairly good ding before the skid went on. Interestingly, the oil pressure went up just a bit past center and also now the motor needs an extra quart or two of oil to get it to read right on the dipstick.

    I've been puzzling over this for a while before I take it back to the shop. I just can't figure why it only happens after the engine warms up and only when at idle. Odd also that it is less prominent when the vehicle is on an incline.

    These are a few thoughts and ways I can test this.[list=1][*]Oil pump pickup is vibrating against bottom of pan (?related to dent in pan?). IIRC, the pickup is metal. If it is plastic, it would not explain this harsh metallic clanking rattle. Why would this vary with engine RPM's?[*]The dent in the oilpan is causing a vibration on the dipstick. The dipstick goes in easily and seats without any resistance. I will pull it out and check the tip for any unusual wear. Still difficult to figure out why it should read that it needs more oil than necessary. I would have expected the oilpan capacity to go down rather than up! I suppose I could replace the dipstick with a plug and see if it makes the rattling go away. Still doesn't explain the low RPM only phenomenon.[*]Engine knocking. The mechanic applied a diagnostic box to the motor but didn't detect anything wrong. I will experiment with higher octane fuel perhaps. I haven't noticed any unusual detonation or continued firing when I switch the ignition off.[*]Motor interference with something metallic. I will get into the engine bay and under with a flashlight after work and look closely for any intereference. I would expect this sort of intereference to be continuous rather than only at low RPM's.[/list=1]

    Thanks in advance for applying your grey matter on this perplexing problem. Any input is appreciated. I will let you know what turns up.
    Last edited by jmbrowning; 05-10-04, 03:24 AM.
    Quis custodiet ipsos custodes?
    2003 TJ Rubicon: 4.5" OME coils; RE SF2; NthDegree TT/oilpan skid/shock shifters; FXD rock rails; Anti-Rock; 5150'

  • #2
    I'm not sure which skid your running but I'd bet that may be it. try putting some sort of hi temp rubber mat between your oil pan and the skid.

    as for your oil level it might be from the fact that you engine angle is changed due to the belly lift.

    fyi, the oil pickup is metal.

    good luck and again... pics???

    "in the end... the rocks always win."


    • #3
      Check your fan, is it hitting the shroud?, I know after putting a lift on mine its pretty close to it.


      • #4
        Found it. One of the manifold pipes was just a few umpteenths of an inch away from the front driver corner of the oilpan skidplate. When the header warmed up it would interfere with the skid plate causing the clanking racket.

        The Nth Degree stuff is really nice but spec'd to pretty tight tolerances. A little tightening of the manifold nuts and careful "adjustment" with a crowbar took care of it.
        Quis custodiet ipsos custodes?
        2003 TJ Rubicon: 4.5" OME coils; RE SF2; NthDegree TT/oilpan skid/shock shifters; FXD rock rails; Anti-Rock; 5150'


        • #5
          glad to hear it! i love when people can resolve their jeepin problems.
          B R E T T
          87 XJ 3" lift, 31s-thats all thats worth mentioning


          • #6
            Rite on