manifold riser

[johnvb1014]

About a year ago the Nissan diesel on our 27 overheated and it turned out to be corrosion in the riser. It was cleaned out at that time and has been in use since, but I thought it was time to replace it and had Marine Manifold in E. Farmingdale NY (631-694-9069) build another. The inner piece on the replacement is copper. As the attached photos show, the base on the replacement is solid without the openings to the water side as on the old. It appears the only thing keeping water out of the exhaust on the original design is the thin rib between them and the gasket. Replacement was $750. Kind of pricey but it should last longer than I will.

John VB

[don123]

The price doesn't sound that bad to me

Yanmar used cast iron mixing elbows on most of their marine engines for many years and they had to be replaced periodically as they all eventually rusted out, though the design didn't allow seawater into the engine even when they failed. You just had a bad leak which I suppose could have sunk the boat if you didn't catch it. Luckily, the exhaust note changed drastically when this happened, so you had plenty of warning that something was going on. I replaced the mixing elbow on the 3GM30 in a sailboat I used to own twice and as I recall, they ran about $300.

The rebuilt 4JH3-HTE that I recently bought to install in my 27FC originally came with a cast iron mixing elbow and this engine had that replaced with the 'new and improved' cast bronze piece. Buying one of those should make you think your $750 is a heck of a deal. My elbow (Yanmar P/N 129472-13501) lists for $1,358.44

They also replaced the old model cast iron heat exchanger with the new cast bronze unit (Yanmar P/N 129693-44901) and that piece runs a cool $2,925.87

Your $750 was a good investment indeed when you consider what happens to the engine when one of those springs a leak

Don

[Tahoma]

I've had an conversation with another 27 owner with the Nissan engine about the factory manifold riser. He removed the factory unit and found it to be a problem. I replaced mine about 3 years ago with the same product mentioned above.

Don't be fooled by an external examination of the factory riser on your Nissan engine.

Unfortunately, you can't tell the condition of the exhaust elbow from the outside. Take a look at the posted photos of the elbow in the earlier post in this topic.

You will see an inner square port where the exhaust exits and outer square passages where the raw cooling water resides. The failure occurs when the raw cooling water eats thru the inner cast iron wall, enters the exhaust port and then has access to the combustion chamber byway of the exhaust valves.

An additional problem is blockage at the round end of the elbow where the exhaust hose is attached. If one removes the exhaust hose one can see the inner port where the exhaust enters the hose and the passages where the cooling water exits. On my engine, the lower 1/2 of the cooling water passages were totally blocked with corrosion which reduced the amount of cooling water that flowed thru the system resulting in higher engine temperatures.

If your boat has spent it's life in fresh water the corrosion would be less than if the boat has spent its life in saltwater and the exhaust elbow will last longer and the engine will run cooler.

I am aware of one saltwater Nissan engine killed by exhaust elbow corrosion and the original elbow on our engine was significantly blocked at the round exit and the wall between exhaust port and the cooling ports on the square end were significantly corroded.

I am glad that I replaced the factory cast iron elbow with the aftermarket unit.

The factory unit I removed from my Nissan has sat in my shop and slowly continued rusting away -- it has cracked into pieces just sitting there.

Save your engine!

Jim

[Roy]

Everyone who has a Nissan LD28 engine used in salt water should do themselves a favor and make an investment in a new riser made of cupro-nickel. Yes they are expensive, but the engine will by far outlive the boat if it has one of these. Consider it as an investment that will last a very very long time--maybe forever. I had two iron risers that lasted only five years each. The cupro-nickel one is 17 years old and still going strong and may never need replacing. The engine should have come with one of these to start with.

[Halcyon]

National Marine Exhaust in Marysville WA just made new wet elbows for my Yanmars.
Nice quality and SS should outlive the cast iron. All for a bit less than factory parts.
Nice easy folks to deal with, maybe they can help you.

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[DesertAlbin736]

Any idea what the typical life expectancy of a stock Yanmar cast iron riser is? I just bought a '71 A25 (see newbie post above) that was re-powered in 1987 with a Yanmar 3GM30F two owners previous to me. The boat likely spent the last 3 years of the '80s in Florida, then from 1999 to about 2000 was up in Ontario, Canada being used on the Canadian side of Lake Erie. Then that owner died. The fellow I bought the boat from bought it in 2001 from the estate when the engine had about 2500 hours on it. He put another 500 hours on it from 2001 to 2012 with a mix of fresh water local lake boating in Idaho and on Lake Powell in Utah, plus several trips to the San Juan and Gulf Islands in the Pacific NW.

Our first run with it had some overheating problems when running sustained at 3200 RPM, but that seemed to be related to a leaking raw water strainer, with the raw water pump having a hard time priming itself. I've since repaired that and put a new pump impeller in and plan to test run it again in fresh water at Lake Pleasant near Phoenix. Now it's got me thinking I should pull the exhaust hose and see what the inside of the riser is like.

[eseyoung]

The issue with the Nissan is that when the elbow fails it dumps sea water into the manifold, which causes catastrophic damage to the engine. The elbow almost looks like it is something that you may use for a raw water cooled engine and is a generally poor design for a number of reasons (no zincs?!!), anyhow.

as for the speculation as to weather or not yours is in need of replacement it would be a wild guess.

the good news is, your Yanmar, i don't think, is made that way, so its not as big of a deal if/when it fails. If you aren't having any issues with over heating or leaking water/exhaust i wouldn't worry to much with it. I have heard of others failing on Yanmars from my understanding is that when they do the boat can still move and be returned to the dock under its own power. but if you need the piece of mind and have an extra grand by all means do it.

[don123]

Any idea what the typical life expectancy of a stock Yanmar cast iron riser is?

I had a 3GM30F in my sailboat and the first replacement of the mixing elbow was shortly after I bought it at about 1100 engine hours. I went through a second one 5 years later at about 750 additional engine hours - Both times it leaked water and exhaust (no harm to the engine, as mentioned above) and both times I put a temporary patch on it using Marine-Tex epoxy. Smelled bad, but lasted until the replacement could be installed

I have a 4JH3-HTE in my 27FC and when it was rebuilt, they replaced the cast iron mixing elbow with a new factory part which looks identical except that the new one is made of cast bronze. I would check and see if they make a bronze replacement for the 3GM series - If so, buying one of those would be the last one you'd ever need

Our first run with it had some overheating problems when running sustained at 3200 RPM, but that seemed to be related to a leaking raw water strainer, with the raw water pump having a hard time priming itself

If you need to run a sustained 3200 RPM to achieve hull speed, you might look into a slightly larger prop or one with a bit more pitch. The 3GM30 in my 34', 15,000 pound sailboat would push it to 7.5 knots (slightly above hull speed) very easily at 2700 RPM and the max engine speed under perfect conditions was about 3200 . . . . which made more wake, but not much more speed. I'm guessing your transmission on the Yanmar is geared lower than the one it replaced and if they didn't calculate the correct prop for it when they repowered, you might find both better performance and lower fuel burn with a better matched prop. A larger diameter (if you have the room) will be more efficient than adding more pitch

Don

[Tahoma]

I watch the engine temperature and replace the Yanmar 3GMD cast iron riser when the temp rises significantly. FYI you can beat the price of the Yanmar riser with an after market one made by an outfit in Vancouver, B.C. Also one can find stainless steel risers on ebay. (The Yanmar is our Puget Sound sailboat. Our Albin 27 now in Florida has one of the Marine Manifold units pictured on the photo in an earlier post.