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Engine knocking on cold startup: 2001 tahoe 5.3

Discussion in 'General Chevy & GM Tech Questions' started by calvinh39, Apr 26, 2012.

  1. calvinh39

    calvinh39 New Member

    I have a 2001 Tahoe Lt with a 5300 Vortec engine with 89000 miles. I have this problem when I first start it after it has been sitting overnight it has a knocking noise but it goes away in about 40 seconds. Do anyone know what might be the problem with the engine. Leon
    Last edited by a moderator: Apr 26, 2012
  2. moogvo

    moogvo Moderator 1000 Posts

    Sounds like an oiling problem in the bottom end... Could be caused by crud in the oil passages, weak/clogged oil pump/screen or damaged/worn out connecting rod bearings on the crankshaft.

    Can you give us any more details?
  3. osgprometheus

    osgprometheus New Member

    Go to an automotive parts store and pick up an automotive stethascope. Have someone start it cold, and listen to the oil pan.
  4. calvinh39

    calvinh39 New Member

    The oil and filter is change ever 3000 miles the oil pressure seems to stay above 45. This started about three months ago. I started the vehicle this am and was not able to detect any knocking. I seem to hear the knocking better when I am inside the vehicle the knocking stops around 40 seconds.
  5. moogvo

    moogvo Moderator 1000 Posts

    Are you sure it is from the engine? I had a cat on my '03 that "Knocked" on startup. It actually sounded like someone was behind the dash knocking on the bottom of the firewall.
  6. calvinh39

    calvinh39 New Member

    Are you talking about your catalytic converter?
  7. moogvo

    moogvo Moderator 1000 Posts

    Yes. I had the transmission rebuilt. When they took the exhaust pipe off, they dropped it on the floor. It broke the internals of the catalytic converter. It wasn't bad enough to set the light, but I could hear it knocking and tapping.
  8. osgprometheus

    osgprometheus New Member

    My old mans truck it doing pretty much the same thing right now. It is a heat shield though. When the idle is low, or cold it rattles. It seems that when the bolts warm up, it tightens up on the shield and stops the rattleing, or knocking sound.

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