Dry-Joint Exhaust ??

Discussion in 'General Discussion' started by 37 Dancer, Jan 6, 2009.

  1. LG111

    LG111 Member

    250
    Jan 4, 2015
    NW
    410
    8.1
    Something to note on the 8.1S exhaust system than generally doesn' get mentioned. The bottom of the manifold has a drain. This allows the entire system including the heat excangers (water, oil and trany) to drain dry. Hence, why there is no zincs on the 8.1s. Which also helps with extended life. Ever look at the side exhaust on first start and it takes several seconds for water to spit out. Well that's why.... the system is refilling.
     
  2. M Prod

    M Prod Active Member SILVER Sponsor GOLD Sponsor

    139
    Oct 6, 2017
    North Vancouver, BC
    2005 340 Sundancer
    Aquapro Dinghy w/ Honda 8hp
    Kohler 5KW Genny
    Raymarine C80
    8.1 Horizons /V Drives
    That’s handy. Does it just drain into the bilge?
     
  3. LG111

    LG111 Member

    250
    Jan 4, 2015
    NW
    410
    8.1
    No, out the drive or out the shaft seal depending on your set up. Lowest point out to sea level.
     
  4. M Prod

    M Prod Active Member SILVER Sponsor GOLD Sponsor

    139
    Oct 6, 2017
    North Vancouver, BC
    2005 340 Sundancer
    Aquapro Dinghy w/ Honda 8hp
    Kohler 5KW Genny
    Raymarine C80
    8.1 Horizons /V Drives
    Ah, ok. I always wondered about why it took a few seconds before it started ‘spitting’. I also was hoping the draining was going to be a simple explanation for the water that’s always in my bilge (even a day after sucking it all out) but that’s a different thread. :)

    Thanks! I’m going to sleep better tonight. :)
     
  5. Jimmy Buoy

    Jimmy Buoy Active Member

    Dec 3, 2008
    Sarnia, Ontario, Canada
    340 Amberjack
    twin 8.1S 370 Hp + 4.5 Westerbeke Genset
    There have been issues with 8.1's of engine damage from leaking manifolds, so they should still be checked periodically. The main problem was with the all aluminum manifolds that were being used all the boats - either fresh water or salt water. The salt water boats had issues due to the salt water corroding the manifolds from the inside out (rather quickly). Some got lucky and the corrosion hole would show on the outside of the manifold which could be spotted by a watchful eye in the engine room. Others weren't so lucky and the corrosion hole was thru to the exhaust gas side of the manifold causing water to drain back into the exhaust valve areas upon shut down. This caused exhaust valves to rust and could also be enough water to hydrolock a cylinder if the exhaust valve was left open upon shut down. Once the engine was restarted with a cylinder full of water - BANG! Engine ruined.

    Now, with cast iron manifolds the time it would take to have the same corrosion problems is longer vs aluminum, but not eliminated. In time, the cast iron ones could still leak internally due to corrosion and cause the same issue. Don't be thinking that a "dry joint" exhaust will never have internal water leakage problems - they just won't leak from the joint - instead it could be a pinhole through the casting caused by corrosion.

    I operate in fresh water and have the aluminum manifolds and am confident that they will last 20+yrs. You may want to get other's opinions as to the expected longevity of cast iron manifolds in salt. From what I've seen in other posts, it is difficult to inspect these manifolds for future corrosion issues within the chambers. Once they leak, the damage is soon to follow!
     
  6. scoflaw

    scoflaw Active Member SILVER Sponsor

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Interesting how aluminum exhaust manifolds corrode quickly in salt, but the aluminum Y pipes don't ?
     
  7. LG111

    LG111 Member

    250
    Jan 4, 2015
    NW
    410
    8.1
    Big part of the problem was the drain on the aluminum water rail below the aluminum manifold had a stainless fastner. Now mix aluminium, stainless and salt and you have a very basic battery. The result is a plugged drain due to heavy corrosion and then the saltwater could not exit the rail or manifold exasperating the battery effect.. I went thru this when I got my 410. From fresh to salt and in 6 months water rails were shot and major pitting in side the manifold. Changed all to cast and all good. I plan every 6 years to change the manifolds due to saltwater. Just the price of saltwater cruising.
     
  8. M Prod

    M Prod Active Member SILVER Sponsor GOLD Sponsor

    139
    Oct 6, 2017
    North Vancouver, BC
    2005 340 Sundancer
    Aquapro Dinghy w/ Honda 8hp
    Kohler 5KW Genny
    Raymarine C80
    8.1 Horizons /V Drives
    Thanks ...this is exactly why I am concerned. Not because I have aluminum, but I am pushing sea water through a cast iron manifold so corrosion is bound to happen eventually. That and I have no idea how old the iron manifolds are. I will talk to my mechanic this spring and go with his recommendations.
     
  9. LG111

    LG111 Member

    250
    Jan 4, 2015
    NW
    410
    8.1

    If cold saltwater then 5-8 years. Warm saltwater slightly less.
    If freshwater up to 20 years.
     

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