Exhaust Elbow Life vs. Fresh H2O or Salt H20 Duty

[rardiH36]

I am wondering if exhaust elbows on boats operated in fresh water last any different than in salt. Maybe the way to pose the question is: For you fresh water only guys/gals, are your exhaust elbows corrosion free after many years? Any info helpful.

Reason for asking is that I replaced about a year ago my Yanmar 2QM20 exhaust elbow which had coroded through along the salt water injection portions. Besides the cost and hassle of replacing again in the future, I'm also somewhat concerned that in another several years, maybe Yanmar won't even be supporting the part. I know that some owners of salt seawater cooled engines add a diverter valve to tap into their fresh water supply and run the engine for a minute or two with fresh water to flush the salt water through before shut-down. Although my engine is cooled with self contained anti-freeze coolant through a heat exchanger, I'm thinking that adding fresh water flush capability to the raw water side might greatly extend the life of the exhaust elbow -- and the heat exchanger in the bargain.

thanks
rardi

 

[sailaway78]

The ultimate answer

I think that the ultimate answer to exhaust elbows is to have one custom made out of stainless. They are not particularly complex, nor that difficult to make. A good machine shop should be able to make up a stainless elbow, for not a lot more than the cost of a "genuine" Yanmar elbow. I saw one Friday, made for a big 3208 Cat diiesel, that looked pretty good, and don't think that one cost nearly as much as a factory replacement.

 

[RichH]

Re: The ultimate answer

Black Iron will be more corrosion resistant than stainless in any 'wet & exhaust gas' application. Cast Iron is the best.

The change out frequency depends on how 'hard' the water is and HOW HOT the water is coming from the exhaust manifold. Fresh water has less 'dissolved carbonates' than sea water ... in most places, but not all.
If the fresh water is coming from an area that has mostly limestone formations, and the usual 'acidity' (low pH) of the rainwater for that area is high, ... all bets are off.

 

[Stu Jackson]

rardi, you might be over-thinking this a bit. I know many folks with our C34 boats in salt water. About 7 years ago one of our local SF guys thought to ask how many years folks' exhaust elbows lasted. Then the conversation turned to engine hours. #s were all over the place, from 608 to 1404 (me) [my boat was 15 years old at the time] and some longer, some shorter. Part of the issue is what they were made of, as Phil says, SS may be considered by some to be superior. Everybody's got a different tune: http://www.c34.org/faq-pages/faq-exhaust-pipe.html

So much has also to be with general maintenance attitude of the skipper, care in regular inspections, engine type of use (12 seconds without warm-up, vs. regular hard running), and the like.

The freshwater flush seems to be an unnecessary complication. If it was my boat, I wouldn't bother. I haven't! But think of it like reefing, if you even think the riser is questionable, replace it and sleep better for the next five years (at the very least).

My other impression is that our Universal exhaust risers are separate from the engine and the injection nipple is pretty far away, whereas my understanding of Yamars seems to place them right on the engine, where they have been reported to "cake" up. I've checked mine and it's clean as a whistle from the water pumping through. Same hot exhaust and hot water, but a different location and perhaps a different configuration.

The failure reports on our risers at near the nipple, but not always "THE" nipple, like mine, which broke right above the nipple. And the new one.

 

[redhead78]

Hey all, I guess the $208.00, upgrade for the high rise ss exhaust elbow was a good deal after all. When I bought the new 35 beta there are lots of option upgrades like when you buy a car. I chose the 100 amp alt,over a 60 amp, custom width mtr mts, high rise ss elbow, waterproof control panel. After the initial price then you start adding its kind of overwhelming, however, important as you can see the value of an item as simple as an elbow. As a carpenter, along time ago, I learned that quality will stand the test of time. Red

 

[Caboteur]

2qm20?

If this was the original elbow it was there for the better part of thirty years... they went to the 2GM20 in the early 80's. Let's go all out and say 25 years! That should bring us to 2035? Will the rest of the boat still be around? I'll be 85; I wouldn't worry about it!

Pierre le Caboteur

 

[RichH]

BTW & FWIW
Most Yanmar dealers carry (under the counter) Westerbeake cast ALUMINUM Injection nozzles. This coupled with a Yanmar manifold exit 'adapter' casting (manifold flange to threaded 1.5" NPT for black iron pipe (on the shelf) and using standard plumbers threaded 1-1/2" black iron pipe, elbows, nipples will result in a 'superior' injection nozzle, one that can be so arranged that the level of the actual injection nozzle portion is MUCH above the boats waterline.
Cover the 'piping' with heat resistant plumbers lagging-insulation .... and you have a 'dry stack' that wont allow 'drain back' in rough seas.

 

[rardiH36]

Thanks for the info. Yes Stu, I probably am eroneously over-thinking and adding unecessary complexity.

Next time, I might explore a custom SS job. Or as RichH suggests, cast iron/black pipe. On this, the threads of hardware store galvanized iron pipe actually come close enough to get 4-5 or so full turns into the engine's female fitting. Then a 45 degree fitting to get the downward angle for a second piece of pipe. A smaller tube could be welded into that for the mixing of the seawater.

Here's a pic of my old elbow which I replaced with a new one exactly the same. It's cast iron. Similar cracks to the one you see are on the other side and bottom as well. On an inspection of the engine one day, I noticed the begining of a crack and some indication of rust. I replaced it pronto. It was only after I removed it from the engine full extent of its remaining fragility was revealed. Actually the cracks have been getting bigger while the elbow has been out in my backyard.

 

[RichH]

If you have cracks like this on the injection elbow tail ..... you'd better soon do a complete inspection of the exhaust manifold - both on the 'gas side' and the 'water side' .... plus a pressure hold test to make sure that the manifold isnt leaking BETWEEN the water side and gas side.
:-O

 

[Steve Dion]

The answer regarding fresh water and the mixing elbow is that they usually do not coke up and corrode up in the delta. I swapped mine out after about 10 years and there was very little carbon and no visible signs of interior corrosion.

My understanding is that they normally last about 5 years of normal use in a salt water environment.

I think that the reaction of salt water and exhaust gas causes then to coke up and corrode.

 

[Stu Jackson]

My understanding is that they normally last about 5 years of normal use in a salt water environment.

I think that the reaction of salt water and exhaust gas causes then to coke up and corrode.

Steve, my experience simply has been different. The exhaust riser on the 12 year old boat I bought in 1998 had no evidence of every having the elbow replaced by the PO and it lasted for another few years to 2003. Maybe the Yanmar engine elbows are different, as I mentioned before. Mine's still working after these 7 years. Our old one never coked up either - the break was in the picture I posted, but both tubes were clean as a baby's bottom...

rardi, here's a flick of a friend's idea. He did it in his garage on an M25. Not a bad idea though if we can fit the concept on our boats, much easier to deal with. Of course, he wouldn't use these materials on his boat, but the concept is cool

 

[Steve Dion]

Stu: The design of the Yanmar is much different. I do not know why the elbow on the 2GM & 3GM are designed like they are, but the 1GM is more like the one on the Catalina (Kabota).

It may be that the "elbow" effect slows down the exhaust gas flow or something. I am assuming that the QM engine is very similar to the GM.

http://sbo.sailboatowners.com/index.php?option=com_mtree&task=viewimage&img_id=7019&Itemid=257

 

[rardiH36]

The QM exhaust elbow arrangement is very different from the GM series.

See the pic of the QM drawing. I've drawn a dotted line on the elbow piece. It represents that inside the elbow, is a separation "shelf" to keep separate the water injection and the gas exhaust near the manifold. The separation is open near the bottom end of the elbow fitting where the water and gas mix at that point. I suppose this arrangement gives added protection against water being able to back flow into the exhaust manifold.

For RichH: Yep, I've thought about the exhaust manifold. However, two differences compared to the elbow: 1) The outside of the manifold remains shiny Yanmar grey paint in great condition. Absolutely no signs of rust or cracks or imperfections anywhere on the surface. But of course I can't see the inside of the exhaust gas chamber. 2) Anti-freeze coolant circulates through the exhaust manifold cavities rather than salt water. I'll take another hard look though. The exhaust manifold I've read is extremely difficult to find. And very expensive. Failure is not a good scenario.

 

[kloudie1]

Rardi, quick note.. My original elbow ('85 3 GMF) was in salt water service exclusively.. (Marina Del Ray, Ca. and Houston, Tx) it plugged in 8 years and rusted through completely in 3 more years (11 yo) .. The boat now is in a fresh water bayou and gets flushed when I come in from the lake, about a 10 minute motor in fresh water.. Lake pontchartrain as brackish and the Mississippi Sound is not as salty as the gulf .. The new elbow has been in service without cleaning now for 14 years.. I do not know if the wall thicknesses of the two parts was the same initially.. but I do believe that more salt in the water will plug and corrode the ell faster..
Uhhhhh we have some tar helping with the corrosion right now!! ??