Replace Manifolds on FWC engines

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by Todd320, Feb 2, 2018.

  1. Todd320

    Todd320 Active Member

    542
    Jul 21, 2016
    St. Petersburg, FL
    2007 Sea Ray 320DA
    Twin V-drive 5.7L 350 Horizon
    i have 2006/7 5.7L 350 mag MPI Fresh water cooled engines.
    Based upon the parts diagram, appears the coolant is flowing through the manifolds, 2 hoses each side, upper and lower manifold. They should be protected from the salt water. Is there a reason I would need to replace the manifolds, and not just the risers and exhaust elbows when time comes in 2-3 years (last replaced in 2016)?
     
  2. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    the risers are also part of the closed cooled side and should last a very long time along with the manifolds
     
  3. Mightychan

    Mightychan Member SILVER Sponsor

    108
    Oct 8, 2016
    Panama City FL
    2005 DA 420, AB Dink
    Cummins 6CTA
    I believe this is incorrect. My understanding is that the 320 risers and manifolds are raw water cooled (the engine block is FWC) and have a lifespan of about 3 years in saltwater. This is coming from a guy that is currently replacing a seized engine due to riser/manifold failure.
     
  4. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    How do you know the history of this guys motor ?

    Engine number would tell the story. Quite common to have a full system on a small block which would include manifolds and risers. A failed elbow, which is possible, could cause the damage you mention.
     
  5. Mightychan

    Mightychan Member SILVER Sponsor

    108
    Oct 8, 2016
    Panama City FL
    2005 DA 420, AB Dink
    Cummins 6CTA
    I know the history because I own it...or at least have for the last year.
    Engine number OM391389. I believe that the risers are dry, uncooled, so my statement above about the risers being raw water cooled is incorrect. I am under the impression that the manifolds and elbows are raw water cooled, hence both are subject to corrosion and need to be replaced every 3 years or so. But I could be wrong. I am all ears :)
     
  6. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Can tell you right now an OM prefix is not a 2006/7 engine. Don't have time to look up your engine right now and maybe your cooling has been reconfigured by some one else. Easiest and simplest is to pull off a hose or 2 and see what comes out. The system I'm describing a 2006 with a OW prefix will have a closed gasket between the riser and elbow.

    It will also be dry joint. Manifold has an antifreeze feed line, riser has the antifreeze exit line. Elbow will have it's own raw water line.

    Get out your screw driver, won't take you long to figure out what you got.
     
  7. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    I looked that up @ mercruiser parts lookup.com. Your serial number says you have a warm riser if it's stock, which means your manifold and riser has antifreeze in it. If it was my boat I would still pull a couple of lines to look/see.
     
  8. Todd320

    Todd320 Active Member

    542
    Jul 21, 2016
    St. Petersburg, FL
    2007 Sea Ray 320DA
    Twin V-drive 5.7L 350 Horizon
    One engine is OW399140, based upon the diagram (haven’t actually looked at the boat), and not sure I am reading the diagram correctly, manifold has coolant in/out, and elbow has raw discharge. I believe previous owner replaced manifold/risers/elbow just once in 9 years/300 hours.
    My theory is, I just need to keep an eye on the elbow and ensure the blocking gasket between it and the riser stays intact and does not allow raw water to get to the riser/manifold. And since the elbows have raw water going through them, it should be replaced on a regular schedule, 3-5 years, sooner if yearly inspection warrants it??
     

Share This Page

Show Sidebar