Anyone know this Exhaust Elbow?
- Thread starter Roger Long
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Hi had one of these on my Yanmar 3gm30f Would quickly block off, I always give my Engine a rev to blast it out before switching it of, to know avail. I pull it off each twelve months its always blocked. if you think about the design and disruption to flow, once a build up begins it will just get worse exponentially. I have now given up on this design and have put the stock straight "Yanmar" mixing elbow on. I have also noticed she will now rev out to 39000rpm (not under load), something I hadn't seen before. My exhaust, which is above the waterline, runs from the silencer through the back locker and then up to the gunnels before dropping back down to the outlet, have run this setup for 6 months now with no problems, obviously I will still inspect every 12 months.
I don't think a "rev" will do it. You should try to get up to 80% power for most of your operation and run at full power for 10-15 minutes each time the engine is run.
80% power is not 80% of maximum RPM due to propeller characteristics. For example, maximum horsepower for my QM Yanmar is 2600 rpm. 80% power is at 2400 for a typical fixed prop so you want to run your diesel pretty hard. 80% power could be at 2100 rpm if I had a controllable pitch propeller.
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I found the elbow at Torrensen with the new part no.: 104214-13521.
It is exactly like mine from a 79 YSM 12 and works with my new 2gm20f, which was and is below the waterline.
Thanks for the link, as I've been looking for one because, as Max von Sydow once said to Robert Redford in Three Days of the Condor, "For that day".
It is exactly like mine from a 79 YSM 12 and works with my new 2gm20f, which was and is below the waterline.
Thanks for the link, as I've been looking for one because, as Max von Sydow once said to Robert Redford in Three Days of the Condor, "For that day".
To answer revs I use I usually run at 2700, cruising along at 7+kts with a clean hull I can and have reved her out to 3300revs but under protest and with little percievable gain in speed about 7.5kts, but som of the bars I come through sometimes you need all the speed you can get to avoid broaching i:e we sometimes experience 2 -3mtr swell coming through our seaway
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Roger, if you are taking the mixing elbow apart, do note the threaded coupling between the bottom standard elbow and top mixing elbow, one has RH thread and the other a LH thread. Don't remember which side is RH and LH thread but I guess you'll find out soon enough.
If you can rev up to 3300, then the shape of a typical propeller curve means that you are only taking about half the horsepower out of the engine in normal cruise at 2700. If you only infrequently load the engine up higher, say when big seas are running in the inlet, that could have been a factor in your coking problem. The sharp bend in your old mixing elbow compounded the problem.
I think you need to take her up to about 3100 for 10-15 minutes every time you go out just to keep the engine happy.
A data point I'd like to help confirm my theory: Did you notice any performance changes of the mixing elbow coking up that led you to inspect it or was the plugging and increased back pressure invisible until you took it apart?
That does look to be the case with the reverse thread in the mixing elbow although mine is buried so deeply that it's hard to be sure.
I looked in the parts manual which is on the boat and this mixing elbow is shown. It just doesn't show up in the service manual. A little more research would have saved this whole thread but, then, we wouldn't have gotten into the other things.
Strangely, the parts manual shows the connection between the street elbow and the mixing elbow in dotted and refers to it as a "pipe" with no Yanmar number. That would indicate that it is a straight pipe nipple of length necessary to get the elbow above the waterline. Equally strange, they do have a part number and will supply the street elbow which appears to be a standard plumbing fitting.
I'll verify the threads when my new mixing elbow arrives in a week or two. (Back order)
Not sure the dotted line pipe thing is so strange Roger. Every boat installation is different and mine has a much longer pipe both from the manifold to the street elbow and from the street elbow up to the mixing elbow.
Still wondering what your water lift muffler installation looks like, my problem is my vetus is mounted on the side of the engine "room" and the hose from the mixing elbow is very inflexible leading to a horrible installation. I need to mount my new vetus so the inlet is directly under the mixing elbow outlet. So I am looking for ideas on how to mount the water lift muffler.
Still wondering what your water lift muffler installation looks like, my problem is my vetus is mounted on the side of the engine "room" and the hose from the mixing elbow is very inflexible leading to a horrible installation. I need to mount my new vetus so the inlet is directly under the mixing elbow outlet. So I am looking for ideas on how to mount the water lift muffler.
It would be strange if one end of the pipe is, in fact reverse thread. This is a place it would make sense for there to be a standard pipe because, as you say, this dimension would be different in each installation.
I'm not sure what kind of muffler I have but it looks like a small shop vac. Maybe an earlier Vertus or similar waterlift. The exhaust line runs about horizontal and slightly downwards. The base of the muffler is about 6 inches above the shaft line near the coupling. Exhaust hose runs out of the top of the muffler, up into the cockpit coaming, and out the transom. The hoses are bent to the max but there weren't good options in the small engine space.
Roger, wouldn't installing an anti-siphon loop eliminate that whole issue? We have one on the water line from the engine to the nipple on the exhaust riser. The nipple itself is below the waterline, the anti-siphon loop is above it. Like Maine Sail's posts on his website about it.
No. The raw water injection has to be downhill from the exhaust or water will run back into the engine with dire results on shutdown or if cranking when the engine doesn't fire on a balky start. I have an anti-siphon loop in the raw water line but that would just make it easier for the water in the hose to flow back into the engine if the injection point were on the engine side of the elbow. It only takes a little bit to cause huge problems.
I don't have a siphon break in my exhaust line itself but the exit point on my boat is quite high above the water (almost 18") and the line loops well above the deck inside the cockpit coaming.
The new elbow arrived and the threads are, indeed, reversed. The reason there is no Yanmar part to attach is that there are semi-commonly available plumbing nipples that have reverse thread on one end and reverse thread coupling to match. These are for use in gas installations where unions are not permitted and it's necessary to finish up a pipe run in the middle.
Nice looking unit. The water runs over the top of the "U" and the exhaust to bottom and it is made so that water can't run back into the engine. However, even the thick divider has hot salt water on one side and hotter exhaust on the other. One small leak in the wrong spot and there could be water running back into your engine. Well worth replacing at regular intervals and before failure.
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