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Silverado is making a knocking noise

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Richmond28, Dec 29, 2012.

  1. Richmond28

    Richmond28 New Member

    Hey my 1990 c1500 5.7l just started making a knocking noise when its idling. I changed the oil about a thousand miles ago and i dont knock what it would be. any ideas?
  2. RayVoy

    RayVoy Active Member 1000 Posts

    Have you checked the oil level?
  3. Richmond28

    Richmond28 New Member

    not yet but i will. thank you:great:
  4. j cat

    j cat Active Member 1000 Posts

    the knock is from all cylinders or just one ?

    the oil pressure/flow if very low will cause the pistons to knock. the main bearings maybe be worn causing a low oil pressure that is the cause.

    another item would be using a cheap oil filter like fram. these have brittle paper filtration some have had filter failure that caused engine damage.
  5. Pikey

    Pikey Moderator Staff Member ROTM Winner 1000 Posts

    x2 on the filter. Don't use cheap fram crap. Only AC delco
  6. TimTom64b

    TimTom64b Member ROTM Winner

    I had something similar happen on my sons truck... Oil filter was plugging causing low oil pressure. Get a quality filter such as k&n, mobile one etc... They have a safety bypass should it plug.
  7. Richmond28

    Richmond28 New Member

    ok so i changed the oil. my old oil filter was a k&n. after i changed the oil, it still knocked. it sounds like just one cylinder but idk what it would be. the oil pressure is fine.:gasp:
  8. j cat

    j cat Active Member 1000 Posts

    the piston could have some carbon causing the knock. put 5 Oz of marvel mystery oil in the crankcase and hopefully the sticking piston will free up...

    with old engines if going too long on oil changes or not changing the oil when hot the sludge can move around after new oil is installed.

    good luck ..
    Last edited: Jan 2, 2013
  9. Richmond28

    Richmond28 New Member

    Thank you. do you know anything about seafoam in the carb?
  10. PantheraUncia

    PantheraUncia Active Member 1000 Posts


    I have used Sea Foam in the gas tank and in the vaccum tube on my truck and it works great. I have never tried Sea Foam in the oil, but I understand it can be done. You need to keep in mind that using sea foam in your oil basically means you are going to do an oil change after running the engine a really short time cause you don't want to leave it in the oil too long.

    Before trying that, make sure you have the correct instructions or you could mess then engine up.

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