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Results 1 to 16 of 16
  1. #1
    Join Date
    Jan 2009
    Location
    Castlegar, BC, Canada
    Posts
    53

    Default 1978 lm318 manifold riser gaskets

    I have fresh water cooled engines with raw water cooled manifolds, risers, and elbows. I recently pulled all my elbows and risers to clean them out and re gasket them. I was somewhat surprised to find that the gaskets only had the round hole at the top open, and the 2 side and 1 bottom holes of the gaskets were solid essentially plugging off the majority of the potential cooling water passages. When looking to order new gaskets I found that they are available with either no water holes, only the top round hole open, or all holes open. As my heat exchanger cooling water exits into both elbows, I am wondering if this gasket set up is designed to restrict some of the manifold flow or to prevent pressure imbalance or back flow? If any one is familial with this set up please fill me in.

  2. #2
    Join Date
    Nov 2008
    Location
    Long Beach, CA
    Posts
    172

    Default Re: 1978 lm318 manifold riser gaskets

    Im not 100% sure, but I think the other passages are for running FWC cooled manifolds. On mine, I replaced the gaskets with only the circle top opening. My manifolds get water at the front of each and at the elbow of each. Mine is a factory FWC engine that pumps the RAW water through the manifolds then overboard through the exhaust.

    will

  3. #3
    Join Date
    Jan 2009
    Location
    Castlegar, BC, Canada
    Posts
    53

    Default Re: 1978 lm318 manifold riser gaskets

    Perfect. Thanks for the input. I generally work on Mercs, but I own a boat with twin Chryslers and love them, but I am not overly familiar with them yet. My instinct told me to replace with the same gaskets that came out, but I wanted to understand how the system works as it is quite different than the Merc or OMC set up. Thanks.

  4. #4
    Join Date
    Sep 2007
    Location
    Bowen, Queensland, Australia
    Posts
    61

    Default Re: 1978 lm318 manifold riser gaskets

    Chris. I have an Australian 6 cylinder, 265cu in, Chrysler Hemi factory marinised freshwarer cooled. The raw water that is used to cool the system passes through a heater exchanger. My raw water is SALT . The water that circulated through the respective part of my heat exchanger , my motor, my aluminum manifold is fresh water. This fresh water does not mix with the exhaust gases that are discharged into my manifold. The fresh water is distributed through the manifold in separate water only chambers. The exhaust gases have their own chamber in the manifold. My system uses a OSCO 689 Riser with two drain provisions on the bottom of the Riser that is bolted on to the manifold. One drains the exhaust chamber and the other drains the other chamber. These are used re winterising and long lay ups. Now this is where it gets interesting. Where is or are the connection points for you raw water that has exited your heat exchanger connect to the Riser or 90 degree elbow ? ? In my system. The most important point , raw water must not enter my manifold from the Riser or 90 degree elbow or any where else ,such as being sucked in where the exhaust gas exit into the water. Hence hydro lock. . Have a think about what i have said. Then we can discuss the position of the two different types of gaskets.

  5. #5
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    6,986

    Default Re: 1978 lm318 manifold riser gaskets

    Chris, without knowing exactly which type of exhaust system you have, I'm going to generalize this since these are all basically very similar with regard to the sea water flow.... I.E., log style w/ rear elbow, or center-rise.

    On a typical Raw Water Cooled Marine exhaust manifold and elbow (aka riser) we'll see several ports between the manifold and elbow.
    The large port will be the main exhaust port, and the smaller ports will be what some of us call the "sea water transfer ports" or "spent sea water transfer ports".

    Queston: When you say that only the round hole was open, are you talking about the main exhaust port, and that the transfer ports were closed off?

    If the transfer ports were closed off, then typically the manifolds will be supplied and also offer a sea water outlet.
    This means that sea water enters the manifold at one area, and exits the manifold at another area.
    Only after the sea water has entered/exited the manifolds does it find it's way to the Elbow or Riser.
    In many cases, the sea water that has exited the manifold, passes throught the T-stat housing prior to making it's way back to the elbow.

    This one shown is a center-rise, but if you'll look at it schematically, it may be very similar to a log style.
    Note that the gasket transfer ports are closed off.


    The transfer ports can be completely blocked off.... or some will be blocked off, yet have a small weep hole in them.
    None-the-less, if this is the scenario (in and out of the manifold and then onto the elbow), and if you were to now install gaskets with fully OPEN transfer ports, the system will become unbalanced, so to speak.

    ***********************

    Now.... if the manifolds are fed at one end ONLY, and if the transfer ports are used to feed the elbows, then these transfer ports within the gaskets must remain open.

    Here's an example of a center-rise exhaust manifold that uses a single supply.
    Note that only one transfer port in this particular gasket is open.
    However, it is just as common to see two and/or all four gasket transfer ports open. (some will even have six transfer ports)




    If you could post photos of your exhaust system and hose arrangement, we'd be better able to help you.



    .
    Last edited by RicardoMarine; 12-08-2012 at 09:51 AM.
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  6. #6
    Join Date
    Jan 2009
    Location
    Castlegar, BC, Canada
    Posts
    53

    Default Re: 1978 lm318 manifold riser gaskets

    I will get some photos of the hose lay out when I get out to the boat in the next few days. The engine is contained coolant system, and the manifolds, risers and 794 elbows are raw or sea water cooled. The manifolds are log style with 6 inch risers out the rear to 20 deg elbows. The manifolds are fed with raw water at one end and the elbows also have 5/8 hoses into them. When I was speaking of the round hole that is open, I am speaking of the 3/4 round transfer port, not the exhaust opening. I was just surprised to see that the 2 side and 1 lower transfer ports were blocked off. I just would have thought that you would want as much flow as possible such as the Mercruiser set up as opposed to restricting the flow to only a 3/4 inch hole. It is possible that it is a balance issue as there is also water being introduced into the elbows just prior to exit with the exhaust?

  7. #7
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
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    6,986

    Default Re: 1978 lm318 manifold riser gaskets

    Chris, I'll look for your photos in a few days.

    Meanwhile, yes, we do want as much flow as possible. However, we don't want to disrupt the "loop" (so to speak) that the sea water makes IF the system is designed to use an Inlet/Outlet at the manifold prior to sending the sea water on to the elbow.

    The OEM has a reason for looping this.
    If we disrutp the loop by using a fully open gasket (where a restricted gasket should be used), we may unbalance the system.

    If you can find OEM information on this, it would behoove you.


    .
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  8. #8
    Join Date
    Jan 2009
    Location
    Castlegar, BC, Canada
    Posts
    53

    Default Re: 1978 lm318 manifold riser gaskets

    Thanks Rick, I will post photos soon on this thread.

  9. #9
    Join Date
    Apr 2008
    Location
    South FLf
    Posts
    55

    Default Re: 1978 lm318 manifold riser gaskets

    Just a question, Why would you not FWC the manifolds and only RWC the risers and elbows? The manifolds will then last forever and you would only have to replace risers and elbows.
    In Answer to your question. when I took apart my 1980 FWC chrysler the first time the OEM gaskets between the riser and elbow were open on the sides and had a 3/4 hole on top. the replacement gaskets only have the 3/4 hole on top. I believe it is just cheaper to mfg. and does not serve as a restrictor.
    Joe
    I wqoe
    Joe

  10. #10
    Join Date
    Jan 2009
    Location
    Castlegar, BC, Canada
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    53

    Default Re: 1978 lm318 manifold riser gaskets

    I know that mine only had the round top hole open on all gaskets, but that being said, I know the manifolds and risers are not original. They have been changed before by previous owner(s). My boat came from the salt but now lives in fresh water so premature manifold degradation is not really a concern.

  11. #11
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
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    6,986

    Default Re: 1978 lm318 manifold riser gaskets

    Quote Originally Posted by joe_l View Post
    Just a question, Why would you not FWC the manifolds and only RWC the risers and elbows?
    Joe, that's what we call a Full Closed Cooling system. With a Full Closed Cooling system, the sea water pump and the Heat Exchanger are larger volume.


    Regarding the gasket arrangement, there are just too many possibilities and configurations to offer a "canned" response.

    We've got ported (sea water ports) manifolds that are blocked off right between the man/elbow, we've got manifolds that use a spacer (aka riser in some circles) and an elbow. These can be blocked off above or below the riser depending on whether the elbow is ported for sea water or not.
    We'll see completely Raw Water cooled manifolds, and we'll see manifolds only that are part of the closed system loop.
    Some elblows are ported, so the riser is not necessary.
    Some elblows are ported, and the risers are also ported being used for a manifold return.
    Some ported elbows still require the ported riser to make the manifold CCS capable.

    This one for example could use a riser (aka spacer) under the elbow.

    If the riser (spacer) was ported, the port and transfer ports could feed a non-ported elbow.
    In which case the gasket between the maniold and riser would be a Block-Off gasket, and the gasket between the riser and elbow woulld be open.

    I could go on....... there's just too many different scenarios.
    Last edited by RicardoMarine; 12-08-2012 at 04:31 PM.
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  12. #12
    Join Date
    Sep 2007
    Location
    Bowen, Queensland, Australia
    Posts
    61

    Default Re: 1978 lm318 manifold riser gaskets

    Chris and Joe . There are two styles of gaskets manufactured for for these risers and elbows. The two hole and one hole. The common large hole in the main section of the gasket is for exhaust gases [ ONLY ] the other hole allows the raw water [ salt , fresh , brackish ] to pass through the manifold and then through the water only chambers in the riser and elbow. If a single hole gasket is used in the system. Then this stops raw water entering the water chambers of the manifold. As so in my system. Now, raw water does enter my riser and elbow and hence is mixed with the exhaust gases once they are discharged from the elbow. In my system scale builds up in my riser and elbow . at some point this restricts the flow of the discharge of raw water . Resulting in engine overheating. Have you ever had your hear exchanger presure tested ? This will show if any of the copper tubes that carry the raw water, have been compromised. Hence would allow the raw water to mix with the fresh water in your closed cooling system. Defeating the purpose of separate water systems. I realise that you may know a large percentage of what i have written. So this is here for general information. I have written previously on using Canola Oil to preserve new cast exhaust components. Manifolds, risers and elbows. Jon. PS. Rick has years of knowledge and experience on marine topics.

  13. #13
    Join Date
    Sep 2007
    Location
    Bowen, Queensland, Australia
    Posts
    61

    Default Re: 1978 lm318 manifold riser gaskets

    Rick. I can not access the pictures. Are there fresh water cooling systems where raw water is used to cool the manifold and is not directly discharged into the riser ? That is, a one hole gasket is used in the riser and elbow system. Jon

  14. #14
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
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    12,334

    Default Re: 1978 lm318 manifold riser gaskets

    There is supposed to be only TWO holes in a new gasket for the riser/ manifold joint: the exhaust opening, and the water flow hole above it. The other three openings are slots required for core removal after the casting operation. (That's why new gaskets have only the two holes.) Ditto the infamous but incorrect termed of "freeze out plug" that has nothing to do with freeze protection: That's where the block casting cores are removed after pouring the block.

    Jeff

    PS: If you FWCool the mainfolds, a stainless plate with gaskets on both sides is used to block off all of the water openings.

  15. #15
    Join Date
    Apr 2008
    Location
    Bradford, Ontario, Canada
    Posts
    215

    Default Re: 1978 lm318 manifold riser gaskets

    heres my 2 cents..mine have the small hole at the top of the gasket to allow the water out, the manifolds are fed from the bottom, water fills the manifold then runs down the brass tube , out through the hole at the top of the gasket & into the riser, I believe its done this way to allow the water to absorb as much heat as possible before exiting into the riser, at 4000 rpm I can rest my hands on my manifolds
    Pete.

  16. #16
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
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    Default Re: 1978 lm318 manifold riser gaskets

    Mine too. The inrared temp gun says 130 degrees or so everywhere.

    Jeff

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