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saildork 01-05-2013 03:03 PM

Another Yanmar Exhaust Mixing-Elbow Question
 
I recently bought a Caliber 33 with the Yanmar 3GM30F engine. In place of the stock cast-iron mixing-elbow was a custom-made stainless elbow. This elbow was about 7 years old according to the previous owner. By now, the elbow was weeping rust at the welds, and the surveyor recommended replacement before I motor out of the yard next Spring.

I've been reading every thread on the subject and near as I can tell, the stock mixing-elbow probably won't last any longer than the custom elbow, and there are many complaints about the carbon buildup, degradation of the cast-iron, etc. on the stock elbow. Structurally, the stock elbow is apparently baffled at its distal end while the custom fabrication is not; thus the exhaust gases exiting the custom piece are hotter than they would be coming from the stock piece. In every other way, there doesn't appear to be any effect on performance.

According to the yard, the cost of replacing the custom piece with another custom piece would actually be quite a bit less than the factory-built elbow. So, any recommendations from the collected wisdom of SailNetters on which way to go?

BTW, my sailing grounds will be Chesapeake Bay.

Ahoyhoy 01-05-2013 11:44 PM

Re: Another Yanmar Exhaust Mixing-Elbow Question
 
As a tech, i have seen all kinds of failures of both, the OE exhaust and the aftermarket equivalent. In my experience, you get what you pay for.
The premature carbon blockage is due greatly to the lack of attention paid to the operation of the engine, and if they are removed occasionally and cleaned it becomes a non-issue. The larger concern with the aftermarket, in my experience, is the material failures both internal and external. It happens most frequently at the welded seams but i have also seen them simply crack along the tubing.
Which ever you decide to use, have it removed and inspected every year or two during your major service. Let someone else have the nightmares.

Faster 01-06-2013 12:45 AM

Re: Another Yanmar Exhaust Mixing-Elbow Question
 
We've gotten many years' service from custom fabricated SS elbows. If you have the access or skills/tools I'd go with another of those.

Minnewaska 01-06-2013 09:33 AM

Re: Another Yanmar Exhaust Mixing-Elbow Question
 
If you remove the elbow annually, clean it out and replace it, is the SS really necessary?

For SS to be effective, it requires the presence of oxygen so the chromium oxidizes and creates a protective barrier. Otherwise, its just brittle steel. Not sure how that would happen inside the elbow. I don't inherently understand the need for a SS exhaust elbow, which typically corrode from the inside anyway.

Has anyone ever thought of using high temp powder coating on the interior of an elbow?

Faster 01-06-2013 11:38 AM

Re: Another Yanmar Exhaust Mixing-Elbow Question
 
Quote:

Originally Posted by Minnewaska (Post 971575)
If you remove the elbow annually, clean it out and replace it, is the SS really necessary?

For SS to be effective, it requires the presence of oxygen so the chromium oxidizes and creates a protective barrier. Otherwise, its just brittle steel. Not sure how that would happen inside the elbow. I don't inherently understand the need for a SS exhaust elbow, which typically corrode from the inside anyway.

Has anyone ever thought of using high temp powder coating on the interior of an elbow?

We've replaced the elbow on our current and previous boat (both "Pathfinder" VW Rabbit based engines). In both cases, the original non-SS elbows were not plugged or built up, but had simply, as you say, rotted from the inside out. The first we built out of SS sched 40 pipe and fittings, and AFAIK is still going strong 10-12 years later.. Our current one was fabbed with thinner walled tubing (to better match the exhaust hose ID) so I'll be keeping an eye on that; it's a year old now.

saildork 01-06-2013 11:54 AM

Re: Another Yanmar Exhaust Mixing-Elbow Question
 
Appreciate the input, guys. The owner of the yard where my boat sits says folks in that area (Beaufort, NC) have had positive results with the SS fabrications and that these elbows have routinely outlived the stock elbow. The boat's previous owner has used this yard for years, and still uses it for another boat he owns, so I feel fairly confident that these guys will do good work.

Fortunately, this boat has great engine access, so I can get to this and other places easily for keeping up with the routine and not so routine problems that may arise.

BenMerc 01-13-2013 01:28 PM

Re: Another Yanmar Exhaust Mixing-Elbow Question
 
I have an even more basic question with a similar concern regarding an older yanmar single 12hp. I found a small leak , or what I thought was a leak coming from the water discharge line from the top of the head, clamped onto a ss inverted U pipe with a teflon double-screen threaded onto a 1/4" nipple at the top of the inverted U...The other line at the fore end of U pipe discharges into the vertical exhaust manifold...I am thinking this is some kind of after market vacuum lock prevention? I originally thought it was a pressure release valve, but after dis-assembly, it is not... water and or air may pass either direction. It is mounted at the upper rear of engine compartment, and appears to drip from the teflon screens ... Questions: Is this what i stated? (after market anti-vacuum lock etc.) if it is , should it be drip leaking ? At first I thought it was the lines, as they were sloppily installed and badly chaffed ( needed to be replaced anyhow) but my question also is, can I remove the teflon breather, add a flexible line and relocate the dripping to a more suitable location. ANY help with this would be great...thanks for any info ...


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