Join Shelby Forums Today

cold start engine knock? - 2007 GT500

Discussion in '2nd Generation Shelby Mustangs' started by ericmuscle, Feb 3, 2011.

  1. Feb 3, 2011 #1
    ericmuscle

    ericmuscle New Member

    Posts:
    3
    Likes Received:
    0
    Joined:
    Jan 17, 2011
    2007 gt500 with 4800 miles. first start of the day in my garage i can hear a faint knock. its not loud and you couldnt hear it inside the car if i started it outside the garage. you can hear it if you get out the car though. i hear it from the bottom of the oil pan. no knock on top of the engine. completely stops once the needle starts to move on the temp gauge. i run the correct motor oil and oil filter also. car runs great and no other problems. anyone else hear this with their car???????
     
    ericmuscle, Feb 3, 2011
    ericmuscle, Feb 3, 2011
    #1
  2. Jun 10, 2011 #2
    Troy

    Troy Member

    Posts:
    15
    Likes Received:
    0
    Joined:
    Jun 10, 2011
    Location:
    Ashland Mo
    Re: cold start engine knock?

    That knock you hear is probably the pistons as they reach BDC. Once the engine heats up the piston expands closing up the piston to cylinder wall clearance.
     
    Troy, Jun 10, 2011
    Troy, Jun 10, 2011
    #2
  3. Jun 13, 2011 #3
    G8R CHOMP

    G8R CHOMP Member

    Posts:
    24
    Likes Received:
    0
    Joined:
    Aug 4, 2010
    Location:
    SoCal
    Re: cold start engine knock?

    Is it regular like what a knocking valve might sound or is it more of a light rattle? If it's the latter, you are probably hearing your clutch. If so, you'll hear it with the clutch pedal pressed. Not so much other times. My 08 was like that. After the tsb replacement with a '10 hydraulic clutch, no more knock. (and no more clutch replacements every 10k miles. )
     
    G8R CHOMP, Jun 13, 2011
    G8R CHOMP, Jun 13, 2011
    #3
  4. Jun 13, 2011 #4
    tradde

    tradde Member

    Posts:
    19
    Likes Received:
    0
    Joined:
    Dec 5, 2010
    Location:
    Southwest US
    Re: cold start engine knock?

    My opinion on your noise is the same as Troy's answer. Forged piston are
    a bit looser when cold to allow expansion when they warm up.
     
    tradde, Jun 13, 2011
    tradde, Jun 13, 2011
    #4
  5. Jun 16, 2011 #5
    ericmuscle

    ericmuscle New Member

    Posts:
    3
    Likes Received:
    0
    Joined:
    Jan 17, 2011
    Re: cold start engine knock?

    so is this knock considered normal then since it goes away when operating temperature?? im aware of the clutch rattle, but its not that.
     
    ericmuscle, Jun 16, 2011
    ericmuscle, Jun 16, 2011
    #5
  6. Jun 16, 2011 #6
    tradde

    tradde Member

    Posts:
    19
    Likes Received:
    0
    Joined:
    Dec 5, 2010
    Location:
    Southwest US
    Re: cold start engine knock?

    It is normal if that's indeed what's making the noise. You might want to
    check with someone else to listen and see what they think. Without
    hearing the noise I am just guessing.
     
    tradde, Jun 16, 2011
    tradde, Jun 16, 2011
    #6
  7. Jun 16, 2011 #7
    Troy

    Troy Member

    Posts:
    15
    Likes Received:
    0
    Joined:
    Jun 10, 2011
    Location:
    Ashland Mo
    Re: cold start engine knock?

    Assuming it is piston knock it is very normal for forged pistons. yes it is annoying, thats why most manufacturers went to high silicon content pistons. They have a much lower expansion rate so piston to cylinder tolerances are tighter.
     
    Troy, Jun 16, 2011
    Troy, Jun 16, 2011
    #7
  8. Jun 20, 2011 #8
    Bushmaster

    Bushmaster New Member

    Posts:
    4
    Likes Received:
    0
    Joined:
    Dec 10, 2010
    Location:
    Austin, TX
    Re: cold start engine knock?

    It's commonly called "piston slap" and has been an issue with all the mod motors (also with some GM LS motors, from what I've heard from some GM friends). I've had it on all the mod motor Mustangs I've owned, though I haven't ever heard it on any 4.6 or 5.4 powered pickups I've had. My '08 SGT does it in cold weather if I give it any throttle within the first 30 seconds or so after starting it cold, so I don't do that - I let it idle down to idle speed before pulling out of the garage, and by the time it's down to idle speed the knock is gone. As mentioned above, it's due to dissimilar materials expanding at different rates and is harmless. My 2001 GT actually did it the worst of any Mustangs I've owned - it would make noise for the first few minutes of operation during cold or warm weather, so apparently, Ford has made progress in minimizing the piston slap.
     
    Bushmaster, Jun 20, 2011
    Bushmaster, Jun 20, 2011
    #8

Share This Page