intake manifold problem

Discussion in 'Gas Engines' started by sunbum, Aug 1, 2007.

  1. sunbum
    Joined: Aug 2007
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: burbank

    sunbum New Member

    can anybody tell me why my 455 intake manifold is heating up. Im not sure what number manifold port they are other than that they are the two middle on each side?
  2. kenJ
    Joined: Jul 2005
    Posts: 349
    Likes: 5, Points: 0, Legacy Rep: 56
    Location: Williamsburg, VA

    kenJ Senior Member

    Intake Manifolds normally don't have cooling water passages in them. They are cooled by the incoming combustion air and engine compartment air. The ends may be a bit cooler because they are more exposed. Can you tell a difference in the head temp between ends & Middle? If yes then I would say you have some clogging of the cooling system that needs to be addressed. Otherwise it might be normal.
  3. TerryKing
    Joined: Feb 2007
    Posts: 595
    Likes: 25, Points: 28, Legacy Rep: 289
    Location: Topsham, Vermont

    TerryKing On The Water SOON

    "Heat Riser"

    Most carbureted V8 intake manifolds have a passage in the center from one side to the other that pass EXHAUST gasses to warm the intake manifold. Sometimes there are small control valves, electrical or otherwise that control the flow.

    Sometimes if the exhaust system is unbalanced side to side (like a plugged Cat Converter) they have unusual flow.

    Many GM 350 engines will show an exterior rusted area on the center of the intake manifold from this heated area. Mine does...

    So this may be normal... or if it is REAL hot and new behavior you may have some unbalanced exhaust back pressure or if there's a control valve it may be stuck open...

    Us old Hot Rod Ford Flathead guys used to block these passages with a nickel (US Coin) in the gasket, to get a little denser mixture.

    Of course, gas was 18 cents a gallon in 1956 :D
  4. sunbum
    Joined: Aug 2007
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: burbank

    sunbum New Member

    Thanks for info on my intake manifold. One thing I forgot to mention is at about 10:30am (when outside tempeture reaches approx. 80 degrees, my boat will act as if Im not getting any gas and die out. I can than after a couble of minutes restat and only reach 2100 rpms. Ive checked out and replaced fuel pump, switched from a 650 to 750 holley, checked the water/fuel seperator, hoses, gas tank.
    The mecanic said somthing must be heating up. Then I remembered the intake manifold gets real hot (water will sizel on it) and yes, the two center intakes (directly under the carb) are rusted. sorry I didnt include all this earlier. still alot to learn. Thanks for your help
  5. stonebreaker
    Joined: May 2006
    Posts: 438
    Likes: 11, Points: 0, Legacy Rep: 42
    Location: Shiloh, IL

    stonebreaker Senior Member

    There's a valve on the heat riser that is probably shot. Not sure what it's called, but normally as the exhaust gas heats up, a thermostatically controlled valve is supposed to gradually shut off the exhaust gas flow to the underside of the manifold.

    The engine dying is what the old guys used to refer to as "vapor lock", if I remember my Olde English correctly. ;) Caused by the gas boiling in the fuel line.

  6. sunbum
    Joined: Aug 2007
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: burbank

    sunbum New Member

    sunbum vapor lock

    :D Hey many thank yous for the info. I'll see how it works.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.