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check risers on v/p 280-gctid352915

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    check risers on v/p 280-gctid352915

    Noticed one manifold running a little hot ( could not hold my hand on it to long ) engine still running normal temp, What should i be kooking for when i remove the risers, Some sort of blockage etc:

    Thanks as Always


    Hey Dan!

    How old are the risers and manifolds? Are they or do you boat in salt water? I have a 280 with a VP SMC 5.7 and have always had one run warmer then the other. I mean, I can place a hand on one (but not hold it there fo rmore than 30 seconds, and the other is cool. It is a bit of the nature of the way the coolong water flows through. I take my risers of yearly and check for deposits and clean them out with a coat hanger to get rid of some of the scale. The mounting surfaces between the manifolds and the risers should be pretty flat and there should be a about 1/4" of "meat" there. My manifolds and risers are 5 years old. I boat in salt water and they look good for a couple of more seasons. I would not be too overly concerend of one is warmer than the other. Now, if you cannot keep your hand on it for more than say 2 or 3 seconds, then I would be looking for a problem.
    Tony, Cape Cod, MA
    Vice Commodore Bourne Yacht Club
    1994 Carver 390 Cockpit Motor Yacht
    454 Merc Cruisers inboards
    2014 10' hard bottomed Dink powered by 3.3HP Mariner 2 stroke


      you described the situation perfectly, risaers and manifolds 7 years old fresh water only, Have never had them apart since they were installed will take them off and clean them out and re-install, thanks so much for the info!!

      Regards Dan


        Common causes for what you are experiencing:
        • May be a riser (or manifold) that is completely done, and needs to be replaced.
        • Riser/manifold transfer ports rusted/corroded and restricting outgoing spent sea water. These can often be cleaned out and made to work again.
        • Sea water supply hose interior delamination. Inspect the interior of these.
        • T splitter on a CCS not diverting spent sea water equally. Not uncommon, and shows up more so as other issues develop.
        • T Stat housing on a RWC system not diverting spent sea water equally.
        • **Riser-to-Y-pipe rubber couplers being clamped over the scalloped areas of the riser outlet.

        **This is one that you'll not find in the OEM work shop manual.

        The OEM couplers are almost always too short. I'd not buy these via OEM p/n.

        When these are too short, they inadvertently become clamped over the scalloped areas of the riser.

        Given enough time, the clamps eventually pull the coupler material into the scallops restricting flow.

        This is a 95mm soft wall hose.

        If you can source this and purchase by the foot, add at least 2" to each coupler length.

        Dan, I'd suggest that you warm the engine up before you attempt to remove any of the riser bolts.

        Crack them loose, and then you can allow things to cool down before doing the actual work.
        Rick E. (aka RicardoMarine) Gresham, Oregon
        2850 Bounty Sedan Flybridge model
        Twin 280 HP 5.7's w/ Closed Cooling
        Volvo Penta DuoProp Drives
        Kohler 4 CZ Gen Set

        Please, no PMs. Ask your questions on forum.


          Having done this on the previous 4 (freshwater ONLY) boats, of which presumably never had manifolds off, it would be a good time to pull, inspect, and clean (if re-usable) anyway. If anything it would be for for piece of mind.

          As Rick said, and one of the first parts you'll start undoing is the large band clamps on the exhaust coupler/hoses. Note that each hose should be double clamped on each end, meaning 4 clamps per hose, and the clamps should NOT be situated over the scallops on the risers or they will impede flow. The second spot you'll be looking for issues is at the gasket between the riser and manifold and the ports/holes at the mounting surfaces. It should be reasonably obvious just by looking at the ports/holes, once apart, if they are clogged up or not, and you can poke them back open again. If the metal is corroded, then that would create a different problem involving leakage of the gasket etc... Feel free to take pictures and post online if you are unsure. Once the riser and exhaust hoses are removed, you'll want to pull the manifolds themselves. Note that the manifolds are notably lighter and easier to work with, with the risers already removed and out of the way. With all parts removed (e.g. risers and manifolds), they are easier to flush as well. They can be filled with sand/muck etc..... so I run a metal probe (e.g. coat hanger or similar) from every possible angle, sticking in as far as possible, including through all openings. Locations would include the gasket surface between manifold/riser, the hose inlets/fittings coming (hoses from t-stat housing), rear drain plugs, and ports at the scalloping. I keep probing until all the junk is out. And in one particular case, I had acorns all over the place, including in the block. That was fun. You will inevitably find rust inside the cooling system, and to an extent it will be considered normal. With regards to fresh water boats, I've looked at presumably original manifolds on 25+ year old boats, and the rust was very minor and nothing more than surface rust (e.g. no large scaling, crumbling, voids, or pieces missing). The original "rough" casting surface has always been present with no degree of flaking or chunks missing or wanting to crumble apart. I'm not saying fresh water manifolds can't go bad, but I think they certainly fair better than those subjected to salt water. Inevitably, even this minor surface rust will be broken off due to the act of probin, and you'll continue to see these little bits get flushed out (and it will never stop, as long as you continue to scrape and poke with a probe).

          Also inspect the hoses coming off the t-stat housing running to each manifold, as well as the fittings on the manifolds that these hoses connect to (though the act of probing will by itself clean them out). The hoses should be clean of any debris and hold their shape (e.g. not kinked or delaminating as Rick mentioned). With those hoses off, also check the openings on the t-stat housing for any debris or clogging.

          All this being said, my description above is not an exhaustive list of all possible causes for a hot manifold, but merely a suggestion to take them off anyway, inspect, clean, and reinstall if reusable. If they've never been apart, you just never know what you might find. Being "hot" is also a bit subjective, and in some cases, such as certain Merc (oops I said a 4 letter word) setups, one riser is often significantly hotter than the other, and it's considered "normal." And then the (Merc) problem will switch sides.... meaning the manifold that was now the hot one is cold, and the cold one is now hot. As another subjective statement, I would say this random riser hot/cold switching sides behavior is not much of an issue with this vintage of Volvo Penta though.