Intake Manifold Cracked at Bolt Heads

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Northstar Engines and System Technical Discussion Discussion, Intake Manifold Cracked at Bolt Heads in Cadillac Engine Discussion; Click pictures below for full size high resolution photos of intake manifold bolts. For my 99 STS, i tightened up ...
  1. #1
    RickyHenry's Avatar
    RickyHenry is offline Cadillac Owners Fanatic
    Automobile(s): 2004 Deville; 1999 Seville
    Join Date
    Mar 2008

    Intake Manifold Cracked at Bolt Heads

    Click pictures below for full size high resolution photos of intake manifold bolts.

    For my 99 STS, i tightened up the Intake manifold bolts and studs to 8lbs. All but one of them cracked the plastic on the intake just around the bolt heads. a The thing is, the bolts kept moving and either my brand new torque wrench is a piece of junk or these bolts just keep drilling themselves into the intake manifold as if it was a knife cutting through butter, without ever hitting the 8lbs mark.

    Could this be causing a vacuum leak in the engine or are the holes where the cracks are too far away from any air passages?

    Because they cracked, maybe the intake manifold isn't seated properly? I think I might need to buy a new one. Repairs on this 99 STS are NEVER ENDING!

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  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
    Automobile(s): White Diamond '03 DHS (with DTS floor shift)
    Join Date
    Jun 2004
    Woodstock Ill.

    Re: Intake Manifold Cracked at Bolt Heads

    It is taking too long to download those pics on dialup. I'll have to look at them at work, but if they are not holding the manifold down, then yes, it could be a vacuum leak. I'd pull them and check the threads before going any farther. If the bolts are turning THAT easy the threads may be stripped and you'll have to Helicoil them if the base metal is still OK.

  4. #3
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
    Automobile(s): 2002.5 F55 STS - 67,500 miles, 2014 Explorer XLT FWD
    Join Date
    Feb 2006
    MD Eastern Shore, Kent Island

    Re: Intake Manifold Cracked at Bolt Heads

    The 10mm bolt torque on your manifold is 89 in/lb which comes out to 5.5 ft/lb. To accurately get to this (light) torque, you need an in/lb wrench.

    A lot of torque values changed over the Northstar model run, so you really need a good Factory Service Manual for your particular car for this type of surgery.

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  6. #4
    tateos's Avatar
    tateos is offline Cadillac Owners Connoisseur
    Automobile(s): 1997 ETC (GAVE TO STEPSON 2011), 2000 DTS (RIP)
    Join Date
    Jul 2007

    Re: Intake Manifold Cracked at Bolt Heads

    I don't think those cracks are a leak point. I too used a torque wrench on those bolts during my HG project and I was amazed how many turns it took.

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