Yanmar Maintenance issue: Mixing Elbow

[cheoah]

Capn Dan, I really wanted to cut mine open last time I replaced it. Thanks for taking the time to post.

I had no idea they were designed like this, although it makes sense.

[ironhors42]

A couple of us guys was talking about exhaust elbow today. What caught attention was, one gentlemen was saying why not try using fiberglass exhaust elbow, there would be no rust, and the heat absortion would be less also. Is this correct thinking of using exhaust elbow of this type and do they made product of this type

[Rakuflames]

Originally Posted by Liam Wald

Capn Dan,
Must be two different versions. The engine was new when I got it.
The way this thing is designed I can't see how it could ever clog.
I am familiar with the cast style like in the pictures above. They make a 180 degree turn.
The one I have is almost straight at 45 degrees like a chute and is either SS or monel.
How odd????
Hopefully someone will be able to fill me in about it.

Liam, honestly, there's nothing odd about it. Next June 2015 my engine will be 3 years old, and I will add a mixing elbow to my store of replacement parts. They get deposits on them, and they develop pinholes and/or cracks. That's just how it is. You might as well complain about tires wearing on a car. When the car is new, the tires are new, but you know that eventually you will have to repace them.

It's the same with a mixing elbow.

[cal40john]

Originally Posted by CaptainDana

The reason for the convoluted waterpath is twofold. 1. 'Aims' the water down the exhaust on the muffler side so that hydrolock due to excessive cranking is delayed or obviated. 2. Spreads out the surface area where the metal comes in contact with the water allowing the water to cool the elbow. These pictures graphically demonstrate that the point where the exhaust-heated metal meets the relatively cool water stream is where carbon will build up.

GREAT POST!!

Agree with point two, but I don't see how point one works. Waterlift fills due to not enough exhaust gas and so eventually backs up into engine. I don't see how aiming the water down the exhaust would slow that. The other style water injection system also aims water down the exhaust so should have the same effect.

[Andrew Troup]

I don't know if this was Captain Dana's rationale, but my inferred rationale for the two alternatives on offer (45 degree vs vertical)

is that in some installations there can be the risk, in big following seas, of the water backing up through the waterlift box to the elbow (at low revs or with the engine temporarily stopped but the seacock still open) - purely from momentum.

It may help if the hose loops between the lift box and the transom, and between the lift box and the elbow, are as vertical as possible, hence orthogonal to the direction of momentum flow. And/or if the waterlift box is close astern of the engine, a vertical elbow may be easier to pipe up.

Don't take too much notice of this: it's based on shallow supposition and ignorant inference. The following, however, might be worth reading, for some:

The stainless 45 deg elbows made by Yanmar are quite affordable, but they do rot out quickly, (in my experience, anyway) from pits which start NOT in the water gallery but in the inside tubing, at the point where the water is meeting the outside of that same tubing.

This is admittedly with salt-water cooled engines, where the water is cooler at this point in the process: my thinking is that the exhaust gases, particularly in the early stages of warmup, will condense at this point on the inside of the tube, and carbonic and/or sulphuric acid will be part of that condensate. Furthermore, the carbon buildup which is copious at this location, might end up being a problem for galvanic action (I say this because the resulting pitting looks quite similar to galvanic corrosion).

Carbon does not always feature on galvanic tables, but it's quite noble. Graphite is theoretically more noble, in fact, than gold.

So anyone putting in lots of hours on a salt water cooled GM series Yanmar might want to consider taking their 45 deg elbow to a stainless fab shop well versed in marine questions, to get a copy made out of thicker-walled material. These generally last almost indefinitely, where the others can sometimes become problematic in only a year or two.

It's important to decarbon the OEM items regularly (with a small but stiff-bristled and aggressive rotary wire brush in a die-grinder or powerful drill motor), and do it vigorously, then check carefully to see if the carbon has been concealing pits which have already connected through, and actually allow a minute amount of seawater in to wet the carbon.

Naturally this will drastically accelerate any galvanic problem, by providing an electrolyte. Of course it will also lead to a salt-water atmosphere in the upper reaches of the exhaust port, and before you know it, your exhaust valves are pitted, and it's not long before you're into more expensive surgery from the downstream effects of that.

[lateral]

So anyone putting in lots of hours on a salt water cooled GM series Yanmar might want to consider taking their 45 deg elbow to a stainless fab shop well versed in marine questions, to get a copy made out of thicker-walled material. These generally last almost indefinitely, where the others can sometimes become problematic in only a year or two.

Right on the money!My 3GM30(F) exhibits exactly what you have described on the 45deg type elbow. The junction of the inner tube with the flange plate failed completely and broke out with little pressure & the thin walled outer pipe had perforations. This was at 500hrs. Over 10yrs though.No water damage to the exhaust manifold.
A new one OEM cost me $150! (And cannot be returned. Basterns.)
I am going to make the next one from sched. tube.
The inner & outer tube look to be 1.5mm. (OEM, but a later design from the cast version)I have the failed one in my office if anyone wants clarification of what happens.

[CaptainDana]

Originally Posted by cal40john

Agree with point two, but I don't see how point one works. Waterlift fills due to not enough exhaust gas and so eventually backs up into engine. I don't see how aiming the water down the exhaust would slow that. The other style water injection system also aims water down the exhaust so should have the same effect.

Good question. The design of the elbow is to prevent backsplashing into the exhaust manifold.

You used 'eventually' in your post, Cal40john. Most WILL eventually fill (resulting in hydrolock) but there is an exception. If installation is such that the exhaust thru-hull is only slightly higher than the water lift outlet and a several inches lower than the highest point in the elbow, head pressure is supposed to cause the muffler to drain naturally before water lock can occur. In this case, one can crank for 10 and wait for 15, and be able to cycle like that until the starter burns up without water locking the engine UNLESS backsplash gets into the manifold. Personally, I'd shut the raw water intake and not risk it.

Bill Shaw's Pearson 28-2 with Atomic 4 is an example of this design.

[Juniper]

Originally Posted by zeehag

cleaning them in muriatic acid works well if it only a clogged section---the owner of the boat i cruised gom had done that -- got him over a year of use after cleaning...

+1

I've done this too, just make sure to flush it well after, I snaked aline through it and hung it over the side for a few hours after. that was 3 years ago still going good.

[DennisM]

This is fascinating information. Thank you one and all. I replaced the exhaust elbow on my 3GM30F three seasons ago and was thinking I could forget about it. Thanks for the heads up. I'll keep my eye on it.

[Rakuflames]

Originally Posted by DennisM

This is fascinating information. Thank you one and all. I replaced the exhaust elbow on my 3GM30F three seasons ago and was thinking I could forget about it. Thanks for the heads up. I'll keep my eye on it.

The reason I intend to include it in my spare parts is that in some places you may be delayed while one is delivered. I know one felllow who had his go to pot in Key West and had to wait for one to be sent there.

Zeehag is right; it can be cleaned up with muriatic acid, but if it is cracked or pinholed, both really common, you'll still have to replace it. It's just one of those parts that wears out. You may be able to nurse it along, but it isn't as sturdy as it looks.

[Capn Dan]

This is what I did when an elbow was not available and I needed to keep going for 2 weeks. Epoxy, gasket material, aluminum blocks and hose clamps. Better than duct tape!

[Liam Wald]

Originally Posted by Capn Dan

This is what I did when an elbow was not available and I needed to keep going for 2 weeks. Epoxy, gasket material, aluminum blocks and hose clamps. Better than duct tape!

That is by far one of the best band-aids that I have ever seen.
Nice work. I would trust that as a temporary repair.

[David M]

I purchased stainless steel risers for my engines (Cummins B-series turbo diesels). Problem eliminated. It's insane that cast iron is used in a hot salt water environment like this. Planned obsolescence to make engine manufacturers more money?

The risers outlasted the last pair of engines. (10,000+ hours) and are now on the second pair of engines. Yes, stainless is much more expensive but it has outlasted probably a number of cast iron risers plus the hassle and expense of changing them out plus the potential for increased back pressure and overheating problems.

In the long run stainless risers have been less expensive.

[Capn Dan]

"That is by far one of the best band-aids that I have ever seen.
Nice work. I would trust that as a temporary repair. "

Thanks, I received my training in the Bahamas and Mexico. Unless I can figure out how to put the two halfs back together (as shown in the first post) I wll need a new one!!!

[cheoah]

Originally Posted by Capn Dan

Thanks, I received my training in the Bahamas and Mexico. Unless I can figure out how to put the two halfs back together (as shown in the first post) I wll need a new one!!!

Uh, ya, I think a new one...

Very good problem solving on your temp fix, I like it...