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When to replace manifolds/risers-gctid358645

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    When to replace manifolds/risers-gctid358645

    My manifolds/risers are 10 years old. 5.7 mercruisers. Its been salt water used with a flush after most cruises.

    Here are what I think my options are;

    Just go ahead and replace them. Probably the safest thing but a couple of boat units and a lot of labor.

    Inspect with a borescope/fiber optics type thing. Not sure if I would see much.

    Take one off and inspect.

    Do nothing since engs and temp are fine.

    Mercruiser claims that starting about when my boat was made (2002) they improved the manifold/riser system and catastrophic engine failures are much less likely. Does anyone know if this is true? I think it was called "dry joint" or something like that.

    Just curious what other "captains are doing".

    Thanks for any input.


    Generally speaking I would say you are at or near the end of their life assuming most use has been in saltwater. One thing to consider is that problems with the exhaust systems leads to much larger problems later on. Say you are out for a cruise and have a major over heating problem and this leads to a warped head or something of the sort. Now you have a much larger(this = $$$) problem than what you had to begin with if you had just performed the regular maintenance boats need.

    I would at least start with a visual inspection, but honestly if you have them off you may as well replace them because often it is difficult to assess the thickness of the jacket within the riser. If this jacket fails and water is sucked into your cylinder it can create some large problems quickly.

    When you go to buy the new ones don't complain about the price, knowing that us diesel owners are spending 2-3K for the parts alone

    best of luck,



      Replace them. Way fewer boat units than the alternative. You are on borrowed time
      John McLellan White Rock BC
      "Halifax Jack"
      1999 2855 383 stroker BII
      MMSI 316004337


        IÔÇÖm replacing mine at this time.

        I think the cost was $980 per engine, including tax, for Crusader 454 fuel injected.

        I believe the old risers have been on for 13 years, not sure.

        When the salt water comes in from the pump, it goes to the heat exchanger then exhaust riser and then the out.

        Everything else is antifreeze cooled.

        The exhaust risers were about 50% blocked, enough to cause the temp difference between the engines of about 3 to 5 degrees.

        Changed the exhaust on the other motor last year.

        10 years is a good runreplace and feel better.


          Mine is 1989 cobra 350. I just removed my manifolds & Risers. 95% plugged. I love my new Barr manifolds & Risers.


            I would consider replacing the manifold/risers soon. I had a 3888 that had been in fresh and salt water. Externally, the manifold/risers looked fine. The previous owner had already bought new manifold/risers....I just had to put them on. The manifold/risers were about 8 years old. Previous owner urged me to replace. While taking off one of the exhaust manifolds, the manifold broke apart. I was amazed at what happened, but very glad I spent the time to replace.


              I replaced mine this past November while boat was hauled out. Really wasnt a bad job. the hardest part was getting them loose from the mufflers.


                When I was running cast Iron units I was told 7 years max You are pushing the limits


                  I had this company make new risers for my engines, and he told me that he makes them for a whole host of engines, and ships a lot to the states. Has any one used them, as his claims about increased performance seem genuine.




                    Here I go again hijacking a post lol.... In fresh water a OMC riser n manifold how many years should last???


                      Don't know for sure Alexirocz, but I just put my 24 year old manifolds and risers back on my new chev. v 8's (fresh water only) By the way, sure miss Ontario, used to run up to Barrie twice a week from Wisconsin for about 14 years till I retired last year. Great people up your way! Go BLue Jays. (except if they play the Brewers)


                        OMG!!! If I didn't read this here, I wouldn't had believed it. You might be the luckiest guy in the world to get that many years out of Mercruiser risers!! Those things were designed to fail rather quickly and were the number one revenue driving force for Mercruisers engine replacement. I've seen so many owners have them fail REPEATEDLY when the boats were still under warranty and certainly afterwards. If it wasn't for these Mercruiser known defects, Volvo wouldn't had been able to compete. They are the SOLE reason people buy Volvo gas engine boats, well that and outdrive corrossion. I don't think they ever changed them because I still see failures on fairly new engines with less than 200 hours. In fact I've pointed out to people that when you go through National Liquidators inventory of repo-ed boats, that most all the gas inboard boats given back to the bank were Mercruiser powered. The fact that they painted them black (so you can't see traces of "issues" when beginning) is pretty much proof they were hiding something. Who paints a engine black?!

                        Yes, it was them who marinized the Hinos, which is why on boats they're black too.

                        Buy some lottery tickets and get some new NON Merc parts ASAP.


                          Man, there are soo many examples of people who were in your position. Trying to get a bit more out of their risers. Why run the risk of $5-7K in new engine costs. Replace them NOW with quality! products. Don't purchase the cheap ones from CHINA. You'll be sorry!


                            If the risers are cast iron, replace them. I didn't see in your original post what kind of boat you have or if it has fresh water cooling. My old 2655 had a partial fresh water cooling system (block only), My old 270DA Sea Ray had a full freshwater cooling system. If you have the partial system, or if it is raw water cooled I would seriously look at risers and manifolds. As pilothouse king said, MerCruiser had a poor design, even when new, the gasket sealing surface (riser/manifold) was only about 3/16 of an inch at best.
                            2002, 3788


                              Thanks for all of the input, I am going to replace them. I seem to be on borrowed time. I will post the condition of them when I get them off. It is a closed loop system but the manifolds are raw water (salt water in my case) cooled to keep the size of the heat exchanger down. Perhaps the fresh water flush system that I use has extended their life.

                              Now to decide cast iron, alum or stainless. I am leaning toward alum if I can get assurance that cast iron block and aluminum manifolds will interface well together. I assume that boils down to the gasket used between the block and the manifolds.

                              Thanks again