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Manifold plumbing

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  • #16
    On Gary’s diagram - For Ford’s - at numbers 20,21 and 22. Where it splits. I had hoses of 2 different lengths on my 302 going to risers running a Sherwood G21 and it overheated. Heard about it and evened the lengths and it was fine.
    '78 20ft Cuddy
    Mercruiser 350 FWC preVortec w/Carb


    • #17
      Originally posted by Pedlyr View Post
      The other thing is make sure the raw water hoses going to the manifolds are the same length. I thought I would clean things up where the raw water teed for each side.No. It all went to the short side.
      Not knowing which raw water pump you have will tell you my experience. Used to have a crank mounted F-6 pump on an Indmar full FWC 351 with 3" manifolds. No cooling issues. New replacement engine was a PCM 351, 1/2 FWC, 3-1/2" manifold system with pulley-mount raw water pump. A non-PCM Hx was utilized. Exhaust hose temps would get hot on one side. The pump is undersized for this configuration resulting in uneven flow and a hot exhaust hose temp, though sometimes port and sometimes starboard hose. Solved the issue by using 1/2" fittings to slightly restrict flow, creating slight back pressure in the RWC side, resulting in even water flow to both sides.
      C Rhodes
      26' Mackinaw - 1990
      351 Indmar (1990-2006: Great Engine)
      351 PCM (2006 - Current)
      Southport, NC