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  1. #1
    Join Date
    May 2010
    Location
    Michigan
    Boat
    Sea Ray
    Details
    1979 240 Sundancer
    Engine(s)
    260 Mercruiser
    Posts
    55

    Riser gasket question

    Just replaced my port exhaust manifold today but now I have a question about the gasket where the riser meets the manifold. There are coolant passages around the exhaust passage and the gaskets have these same cut outs for the coolant but there is a metal plate mounted between these gaskets that doesn't have these cutouts. Just wondering if this is supposed to be like this? Seems like it would restrict coolant flow. I'm thinking it's probably like car engines where flow gets cut off one place with a gasket to ensure proper flow but just want to be sure before I reinstall the riser.
    Here are a couple pics.

    Thanks.

    Riser, gaskets and metal plate


    Manifold
    Bob Kulhanek

    '79 240 Sundancer, 260 Mercruiser

  2. #2
    Join Date
    Jan 2007
    Location
    West coast Vancouver to Alaska
    Boat
    SeaRay 380 Aft cabin
    Details
    380 Aft Cabin 1989 GPS and Charts by Nobeltec
    Engine(s)
    Twin 454 strait shaft
    Posts
    1,445

    Re: Riser gasket question

    If you check the liquid in the manifold you will probably find it is antie freeze and on the riser it is raw water. That is how it was on my engines. I put in what came out and it all worked well.

  3. #3
    Join Date
    May 2010
    Location
    Michigan
    Boat
    Sea Ray
    Details
    1979 240 Sundancer
    Engine(s)
    260 Mercruiser
    Posts
    55

    Re: Riser gasket question

    Nope, it's all lake water not a closed system.
    Bob Kulhanek

    '79 240 Sundancer, 260 Mercruiser

  4. #4
    Join Date
    Jan 2007
    Location
    West coast Vancouver to Alaska
    Boat
    SeaRay 380 Aft cabin
    Details
    380 Aft Cabin 1989 GPS and Charts by Nobeltec
    Engine(s)
    Twin 454 strait shaft
    Posts
    1,445

    Re: Riser gasket question

    In my 2" thick manual they show both fresh and raw water cooling. In the raw water cooling the gasket is open in the fresh it is closed. No idea how your engine would be set up.

  5. #5
    Join Date
    May 2010
    Location
    Michigan
    Boat
    Sea Ray
    Details
    1979 240 Sundancer
    Engine(s)
    260 Mercruiser
    Posts
    55

    Re: Riser gasket question

    This may be a stupid question but what's the difference between fresh and raw water cooled? They sound like the same thing. I understand closed system has antifreeze in a closed system that is cooled by the outside water through a HX. And in an open system the outside water flows throughout the engine for cooling. So what's raw and what's fresh?

    Never mind just answered my question with a quick search. Fresh water is a closed system.
    Last edited by RLKBOB; 07-05-2010 at 12:01 AM.
    Bob Kulhanek

    '79 240 Sundancer, 260 Mercruiser

  6. #6
    Join Date
    Apr 2009
    Location
    PA
    Boat
    SeaRay
    Details
    95 330 hurth v drive
    Engine(s)
    merc 7.4 inboard
    Posts
    373

    Re: Riser gasket question

    if your manifold had the blocking plate, then you are fresh water cooled (anti freeze) , look in your engine for a heat exchanger. if you find the heat exchanger, then go to your marine pats supplier and get the proper block off gasket. then remember to refill the anti freeze, and to burp the anti freeze at thermostat
    95 da 330 2 7.4L Hurth V drives, 6.5 Kohler Gen

  7. #7
    Join Date
    May 2010
    Location
    Michigan
    Boat
    Sea Ray
    Details
    1979 240 Sundancer
    Engine(s)
    260 Mercruiser
    Posts
    55

    Re: Riser gasket question

    Nope, no anti-freeze, no HX. It's raw water cooled, the only hx is for the power steering fluid. I took a few pics I'll post later. There is a little hole in one of the passages on the plate so if there was anti freeze in the engine it would leak out through that hole. Maybe since mine is so old the direction of coolant flow is a little different from the way the newer ones are set up.?

    Looking at the pics now I think I figured it out. There are 3 coolant hoses going to each manifold. One to the front, one to the rear and one to the riser. Since there is a separate hose feeding the riser this is probably why the block off plate is there. If there wasn't a separate hose going to the riser the ports would definitely have to be open between the manifold and the riser. What do you think of my explanation?





    Last edited by RLKBOB; 07-06-2010 at 12:01 AM.
    Bob Kulhanek

    '79 240 Sundancer, 260 Mercruiser

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