Mixing Elbow

Ed Schenck · Dec 23, 2011

That's a good post, food for thought. I can't even remember my 3YM30 hours and will forget to check next time I go to the boat. Which elbow do you have? Mine points down at a 45 degree angle. It does not have the arch in it. I wonder if that makes a difference. We should both add temp gauges I suppose. I sold my old panel with the 2QM20 that I replaced. It was a VDO panel with a gauge for everything. Thanks for the tip.

seadaddler · Dec 23, 2011

Elbo & Temp

Took my boat out for new bottom job and due to shoulder surgery it is still out so back in July before surgery I took the mixing elbo off and apart to give it a good cleaning.
My older 2GM did clog on me and new about it needing cleaning which worked for me back than so any way I did clean the mixing elbo out on my newer 3YM after giving it to a marina shop they took it apart for me making my life easy,I did the cleaning out with many different pick shaped tools and did get a lot of gook out but it was not clogged at all and the Yanmar always ran very good but wanted to keep it from clogging up badly before trouble and also see if it runs any better.
I will see how it runs when I splash this Jan 1 after returning to Florida from NY and also working on adding the parts for a temp gauge when I return with a photo showing how I plan doing so and also plan to drill a hole for the temp gauge at the panel.
I should have taken pictures of the cleaning of the mixing elbo.
Nick

Bill Roosa · Dec 24, 2011

The idiot light is pretty easy to test. purchase an iron pipe plug the same size as the sensor unit, remove the unit and plug the hole so you don't loose anty. boil some water and place the unit in it. It is just a normally open switch that closes when it gets to the correct overheat temp so it should read infinite ohms when cold (terminal to threads) and zero ohms when hot. If that checks out then the problem is in the wiring. To test that just ground the senor terminal to the engine. the alarm should sound. It it does not then tract back the wire grounding at every connection to find the problem part.

Mike H. · Dec 26, 2011

My system quit pumping water. I traced it down to the elbow. I found some information on this site and followed the recommendation to soak it in 100% muriatic acid for about an hour. It came out looking like new. The coke and corrosion eats away the metal, so this technique will probably only work one or two times. I will replace the elbow next time.

Endurance2010 · Dec 26, 2011

I replaced my mixing elbow a few months ago. I traced the raw water clog down to the elbow. The first time I cleared things up with cleaning out the nipple, but the last time the elbow was clogged. There is a very tight area where the exhaust flows over and then mixes with the water. My mechanic told me Yanmar recommends servicing this part every 5 years or so. It seems quite silly though. All new parts were around $300 or so.

--Dan

Roger Long · Dec 27, 2011

MsEmee said:
In talking with the Yanmar folks at Mastry they recommend a new elbow every 250-300 hours, said that is normal.

Bull Pucky!. They would love to sell you a new elbows. I would be putting in my third since leaving Portland last July.

Are you running your engine most of the time at about 90% of it's maximum continuous RPM? (Check the manual, there is a higher RPM at which you can run for an hour. You want to run at 90% of the lower one which will be about 80% power with a typical prop.) Your boat probably has too big an engine like 90% of sailboats so running at that power level will be splashy and noisy. Run the engine in cruise as hard as you and the boat are comfortable with. Try to open it wide up for about 10 minutes each time you run it or whenever you can. Grit your teeth and run it at the maximum continuous RPM for at least 20 minutes whenever you can.

Make sure everything else in the engine is right. If you are doing a lot of idling to make electricity and cool beer and only running the engine a few minutes getting on and off a mooring, Mastry may be right and that roughly dollar per hour cost of new mixing elbows, plus labor, is just a cost of running your diesel too lightly.

Bill Roosa · Dec 27, 2011

So what I hear you saying Roger is all our problems will be solved by running our engines hard?
I know I have always run mine at 45-50% (2300-2500 RPM) power and batt charging/hot water making on the hook (1000 RPM) and the elbow and all is just lightly coated with never a hint of lumpy buildup. I've been doing it this way for a few years now and have never had an issue.

Don't get me wrong though what you say works, I'm just pretty sure it does not work for the reason you give. A properly tuned diesel with SUFFICIENT RAW WATER COOLING FLOW should not carbon up the exhaust.

It is my premise that most sailboat engines have marginal raw water flow as evidenced by the engine temp changing with different power levels.
Now if an enterprising young sailor opened up the exhaust elbow water inlet you not only get rid of all those tiny clog prone holes you get more total water / minute going through the exhaust. Anybody care to guess what exhaust that is really high in unburned fuel does when it is overwhelmed with seawater?

But for those doubting Thomas’s, lets conduct a survey.
What kind of elbow do you have? The multi water nozzle or the single water nozzle type?
Does your engine coolant temp very when you change power levels. Note: changes in the raw water temp you get from the ocean will also cause some engine temp changes. Please try to discount this effect.

Maine Sail · Dec 27, 2011

Bill Roosa said:
So what I hear you saying Roger is all our problems will be solved by running our engines hard?
I know I have always run mine at 45-50% (2300-2500 RPM) power and batt charging/hot water making on the hook (1000 RPM) and the elbow and all is just lightly coated with never a hint of lumpy buildup. I've been doing it this way for a few years now and have never had an issue.

Don't get me wrong though what you say works, I'm just pretty sure it does not work for the reason you give. A properly tuned diesel with SUFFICIENT RAW WATER COOLING FLOW should not carbon up the exhaust.

It is my premise that most sailboat engines have marginal raw water flow as evidenced by the engine temp changing with different power levels.
Now if an enterprising young sailor opened up the exhaust elbow water inlet you not only get rid of all those tiny clog prone holes you get more total water / minute going through the exhaust. Anybody care to guess what exhaust that is really high in unburned fuel does when it is overwhelmed with seawater?

But for those doubting Thomas’s, lets conduct a survey.
What kind of elbow do you have? The multi water nozzle or the single water nozzle type?
Does your engine coolant temp very when you change power levels. Note: changes in the raw water temp you get from the ocean will also cause some engine temp changes. Please try to discount this effect.

Bill,

I have a customer who went through exhaust elbows every 300 hours or so. With a clean elbow he could fill a 5 gallon bucket in about 70-80 seconds, as collected at the exhaust outlet, which when cross checked with Mack Boring this was at designed flow for his motor..

His problem was that he was over propped, as many owners with Yanmars are, and he was lugging his engine, especially when he added the load of the engine driven refrigeration.. We re-pitched the prop so he could hit max rated RPM, with the refrigeration running, and he's never had another plugged elbow. That was about seven years ago. As of last year when he did the bucket test to check flow he was still filling it at about the same rate six years and roughly 650 hours later, on the same exhaust elbow.

In almost every case I've been involved in of frequently plugging exhaust elbows the prop has been too big, the boat over loaded, engine driven refrigeration or a huge alt was added all of which prevented the motor from being able to attain max rated RPM. Yanmars I find really dislike being over-propped or lugged... A fouled injector can also lead to frequently plugging elbows.

Roger Long · Dec 27, 2011

Bill Roosa said:
So what I hear you saying Roger is all our problems will be solved by running our engines hard?

That's what you hear but not what I said.

My exhaust elbow, which was probably 1979 original, had some plugging when I replaced it but it was all on the dry side. Water flow isn't going to effect that very much.

Mainesail is right about over propping. If you see dark grey or black smoke, as opposed to light grey smoke or condensation fog on cool and humid days, before the last 50 RPM, you are probably over propped.

My experience, more limited with sailboats than Mainesail's, is that most are under propped due to restricted prop diameter. If the engine never gets up to proper operating temperature, combustion will also be less efficient. Rings also don't seat as well running lightly so a bit more lube oil works it's way up into the cylinders which tends to burn in the exhaust manifold.

My engine ran easily up to it's one hour rating of 2800 and always sounded a tiny bit hysterical. The governor and not the prop load was clearly stopping it. I had the pitch increased and it topped out at 2700 with clean bottom and boat lightly loaded. Continuous RPM is 2600 and no significant smoking at that RPM which I treat as a red line except for a few minutes of WOT occasionally, especially after a period of very light running. There is a lot of that in the ditch.

With the boat loaded to the gills and batteries a bit low, the engine tops out at 2700. (Note: this older 2QM is a slower turning engine than the newer Yanmars.) The engine sounds much better and there has been a significant improvement in fuel economy. I haven't been able to run careful trials but it's on the order of going from 5 mpg to 6 or 7. I cruise at 2200-2300 when fuel economy is important and 2400 in smooth water when fuel supplies are close at hand.

Load is not the full story. However, the people I am cruising with had a slipping throttle linkage so their engine slipped back immediately to about 1800 RPM and 5 knots. They are new to the boat and diesels and thought this was normal. I convinced them to put a bungee on their throttle lever as a quick fix and run about 1 1/2 knots faster. Over that first day, their engine steadily sounded better and smoother. They said it was like a different engine by the time we stopped.

I later discovered that their crankcase breather line was lead to the air intake which only has a screen on their Universal. It was about 25% plugged. We cleaned that out for another significant reduction in smoke and smoother running.

I know I have always run mine at 45-50% (2300-2500 RPM) power and batt charging/hot water making on the hook (1000 RPM) and the elbow and all is just lightly coated with never a hint of lumpy buildup. I've been doing it this way for a few years now and have never had an issue.

Engine models, and to some extent, individual installations vary. Yours may not be as susceptible as many to carbon build up. Exhaust elbows are not the only consideration in determining the optimum service power profile for a diesel.

Never having an issue after a few years is not the same as never having an issue after reaching he manufacturer's expected time between overhauls. Without careful comparison with other installations, complete records, etc., you might well replace an engine without ever realizing that you were doing it earlier than you might have. That shorter service life = $$$$$.

In the absence of a crystal ball or a lot of service history with similar installations and individual installation analysis, the best thing the owner can do is run the diesel as close to the way it was intended if, big IF, maximum service life is a consideration. Many owners will have the engine outlast them even if 25% or more is knocked off the engine life by light running.

Incidentally, I notice that my engine runs better if I run it at maximum power for a while and then back off to cruising RPM. Ignition is by heat and getting the engine nice and toasty seems to help. Mine is raw water cooled so cooling is a bit cruder than on a FW engine. This effect may not be noticeable on most diesels.

Bill Roosa · Dec 27, 2011

Well yea
Like I said, a properly tuned....... tuning includes making the motor run at the right RPM for a given boat speed and "add on" package(s).
My assumption was the same as Rogers, the boat is properly tuned and still getting elbow clogging. The solution to that specific problem is not to simply run the engine hard. While that works, (if it is stupid but it works it ain't stupid BTW) it is what I call treating the symptoms and not curing the patient.

Roger Long · Dec 27, 2011

Maine Sail said:
In almost every case I've been involved in of frequently plugging exhaust elbows the prop has been too big, the boat over loaded, engine driven refrigeration or a huge alt was added all of which prevented the motor from being able to attain max rated RPM.

Please explain more to me about lugging and its effect on exhaust elbow plugging. I used to design marine drive trains but the boats were so sophisticated for the last 20 years of my career that all that stuff was done by specialists. It’s been a long time since I thought about these things.

Here is how I understand it with a graph from my engine manual (since it’s the only one I have available).

The top two curves show the engine’s allowable power output vs. RPM. The dotted line shows what the manufacturer permits for an hour of operation at a time. For continuous operation (slightly lower solid curve), which would be running 24 hours a day, you must take 1 horsepower less over most of the RPM range and keep RPM 200 below the governor limit. An engine on a commercial vessel with a continuous rating would normally have its governor reset to limit the engine to the 2600 rpm with this power curve.

The bottom curve, in black, shows the manufacturer’s suggested propeller curve. This is the horsepower required to turn the prop at the indicated RPM’s when the boat is going the expected speed. That part of the equation is the big unknown and fudge factor in prop calculations. Calculating the vessel’s speed is not too difficult but the hull slows down the water flow around the prop so that it is in the range of 70% - 90% of speed through the water depending on hull shape. Fatter hulls slow down the water more. Prop experts depend on having a database of vessels to help them guess at this “Wake Fraction” or “Speed of Advance”. Most of prop selection is getting this factor right.

The thin, red prop curve is for a prop very close to what I had on my boat. With lower pitch, it takes less horsepower to turn it at any particular RPM. These two curves could thus be for the same prop with the blades twisted by the prop shop to add an inch or two of pitch as was done in my case. My prop is now very close to the black curve, at least when the boat is heavily loaded.

Due to the nature of a fixed pitch prop, the horsepower required to turn it drops off much faster with RPM than the engine’s ability to provide it. If you had a controllable pitch prop, you could keep turning up the pitch as you slowed the engine down so that you followed the engine’s output curve. This, in fact, is much of the rational for putting up with the weight and complexity of controllable pitch props.

The prop curves actually keep running up towards the top of the paper. If you added even more pitch, you could have a curve which extends above the engine curve at an RPM which the engine’s governor will permit it to reach, or try to reach. However, the engine can’t produce the necessary power above the curve. RPM stops climbing near the point where the prop curve tops the engine curve. The air supply is determined by the RPM and the governor is trying to supply enough fuel to increase it further. Clouds of black smoke, unburned fuel, come out the exhaust and some of it cokes up in the exhaust manifold.

Even with a severely over pitched prop, say one repitched 2-3 times as much as mine, backing off on the throttle will bring the power production back down into the range the engine is expected to produce without problems. You can add a band on top of the prop curves to represent the horsepower absorbed by alternators and refrigerator compressors. However, you are still only over taxing the engine when the combined prop / auxiliary power curve is above the engine output curve. Many people operate their engines like Bill does, at about half power. They would need a whopping amount of prop pitch to get into this regime.

Back when I was doing propeller calculations, I was also playing around with some sailboat designs. It’s very hard to fit sufficient prop diameter into a sailboat. Getting enough prop to absorb the full horsepower of the engine is difficult. A little extra pitch won’t do it. You need to go to 4 blades and wide blade profiles. Just compare the prop on a displacement trawler yacht with the one on a sailboat of similar size and displacement.

Few people operate sailboats at WOT or anywhere near it. There is just too much motion, spray, and noise with the size of engine typically installed. Typical prop curves drop off so fast that I have a hard time believing that overtaxing sailboat engines with a bit too much pitch is common. In the case of an underpowered sailboat that is always run flat out, maybe. But I see far more people running at about half the rated power of their engines. Either I am missing something here or there is another factor at work on engines where reducing propeller pitch cured exhaust elbow coking.

Maine Sail · Dec 27, 2011

Roger Long said:
Please explain more to me about lugging and its effect on exhaust elbow plugging. I used to design marine drive trains but the boats were so sophisticated for the last 20 years of my career that all that stuff was done by specialists. It’s been a long time since I thought about these things.

Here is how I understand it with a graph from my engine manual (since it’s the only one I have available).

The top two curves show the engine’s allowable power output vs. RPM. The dotted line shows what the manufacturer permits for an hour of operation at a time. For continuous operation (slightly lower solid curve), which would be running 24 hours a day, you must take 1 horsepower less over most of the RPM range and keep RPM 200 below the governor limit. An engine on a commercial vessel with a continuous rating would normally have its governor reset to limit the engine to the 2600 rpm with this power curve.

The bottom curve, in black, shows the manufacturer’s suggested propeller curve. This is the horsepower required to turn the prop at the indicated RPM’s when the boat is going the expected speed. That part of the equation is the big unknown and fudge factor in prop calculations. Calculating the vessel’s speed is not too difficult but the hull slows down the water flow around the prop so that it is in the range of 70% - 90% of speed through the water depending on hull shape. Fatter hulls slow down the water more. Prop experts depend on having a database of vessels to help them guess at this “Wake Fraction” or “Speed of Advance”. Most of prop selection is getting this factor right.

The thin, red prop curve is for a prop very close to what I had on my boat. With lower pitch, it takes less horsepower to turn it at any particular RPM. These two curves could thus be for the same prop with the blades twisted by the prop shop to add an inch or two of pitch as was done in my case. My prop is now very close to the black curve, at least when the boat is heavily loaded.

Due to the nature of a fixed pitch prop, the horsepower required to turn it drops off much faster with RPM than the engine’s ability to provide it. If you had a controllable pitch prop, you could keep turning up the pitch as you slowed the engine down so that you followed the engine’s output curve. This, in fact, is much of the rational for putting up with the weight and complexity of controllable pitch props.

The prop curves actually keep running up towards the top of the paper. If you added even more pitch, you could have a curve which extends above the engine curve at an RPM which the engine’s governor will permit it to reach, or try to reach. However, the engine can’t produce the necessary power above the curve. RPM stops climbing near the point where the prop curve tops the engine curve. The air supply is determined by the RPM and the governor is trying to supply enough fuel to increase it further. Clouds of black smoke, unburned fuel, come out the exhaust and some of it cokes up in the exhaust manifold.

Even with a severely over pitched prop, say one repitched 2-3 times as much as mine, backing off on the throttle will bring the power production back down into the range the engine is expected to produce without problems. You can add a band on top of the prop curves to represent the horsepower absorbed by alternators and refrigerator compressors. However, you are still only over taxing the engine when the combined prop / auxiliary power curve is above the engine output curve. Many people operate their engines like Bill does, at about half power. They would need a whopping amount of prop pitch to get into this regime.

Back when I was doing propeller calculations, I was also playing around with some sailboat designs. It’s very hard to fit sufficient prop diameter into a sailboat. Getting enough prop to absorb the full horsepower of the engine is difficult. A little extra pitch won’t do it. You need to go to 4 blades and wide blade profiles. Just compare the prop on a displacement trawler yacht with the one on a sailboat of similar size and displacement.

Few people operate sailboats at WOT or anywhere near it. There is just too much motion, spray, and noise with the size of engine typically installed. Typical prop curves drop off so fast that I have a hard time believing that overtaxing sailboat engines with a bit too much pitch is common. In the case of an underpowered sailboat that is always run flat out, maybe. But I see far more people running at about half the rated power of their engines. Either I am missing something here or there is another factor at work on engines where reducing propeller pitch cured exhaust elbow coking.

Roger,

Years ago when I helped a friend survey we always compared max rated engine RPM with actual during sea trials. Roughly 45% or more of the boats could not attain max rated RPM and were over propped, it's not that uncommon. The under propped boat was more rare but they were out there too and usually were two blade wheels.. The over propped boats were always the boats with the black soot all over the transom and the ones with a new or recently replaced exhaust elbow.

With our Westerbeke just a 250-300 RPM over prop was lugging the engine enough for the transom to have visible soot within an hour of running. This was not determined by just engine RPM I took her to her normal cruise speed at whatever that RPM was with the over pitched prop or about 300 less RPM than we'd normally be turning.

Even at the same hull speed as the properly pitched prop, though with less engien RPM, the boat was producing visible soot. In discussions with Westerbeke it was explained that we were trying to use less hp to move the boat the same speed thus we were loading the HP curve prematurely due to the over pitched prop. Again this was at the same hull speeds we were doing with the properly pitched prop. Backing off the throttle helped some, and was suggested as a temporary measure by Westerbeke until the new prop came in, but was not a cure and we then went slower than we could with the right prop match.

Our engine is pretty big for our boat yet we still cruise it comfortably at about 70-80% of max rated and she is smooth, quiet and just about as soot free as a 3300 hour engine can possibly be.

We had a similar problem with our old Catalina 36 and going from a 11 pitch to a 9 pitch (if I have the number right) made all the difference in the world. I think we were maxing the M-25XP on that boat at 2800 and we needed to hit 3200. Reducing the pitch was like a magic elixir for that motor as it was a tad undersized for that boat anyway. Once again we went from a black transom to very clean.

With our current prop Westerbeke was absolutely insistent that our engine be able to turn max rated +/- 100 RPM and preferably +/- 50 RPM. Once we got the right prop from West by North everything was again fine, no soot, no lugging, and no zipping around the anchorage at 4 knots at idle...

In nearly every case of premature coking of an exhaust elbow I've been involved in it has been solved by taking some pitch out of the prop. On two boats I know of nothing else was done, just some pitch removed and problem solved.

Our engine now has 3300+ hours and has never had an exhaust elbow but is within 50 RPM of what Westerbeke wants to see, without the fridge on. At 2800 hours I took the elbow off and it was nearly spotless inside other than a thin black film, I reinstalled it.

My only regret was not going even a little less on the pitch as the fridge load causes the engine to lug enough to see visible smoke so we need to back off until I get the happy medium.

With RWC you're up against different cooling issues than we are. Our engine will come up to 180 degrees in about 12 minutes at just idle and will be maintained on the engines t-stat opening and closing in normal summer water temps. She runs at 180 no matter what we do to her, even at WOT she is steady at 180. Unless it is early spring or very late fall then she takes a tad longer to get to 180 and requires some load like the fridge if idling at the mooring before heading out.

Roger Long · Dec 28, 2011

Maine Sail said:
In discussions with Westerbeke it was explained that we were trying to use less hp to move the boat the same speed thus we were loading the HP curve prematurely due to the over pitched prop.

Ah, that's the piece that got lost in the mists of memory. As per my explanation about the prop curve being for an assumed speed of advance, the curve moves up and to the left as the boat slows. If you try to bring your engine up to full power tied to the dock, the best the engine can do is produce 2-3 knots of water flow and you will not reach full RPM. The shifting of the prop curve to the left if the boat doesn't get up to the same speed as with a lower pitch prop could bring the over demand regime down into the RPM range people normally operate at.

I see over propping in boats designed for two blade wheels that have been converted to three because of prop walk and other issues is more common than I thought. Modern designs often have more room for props. Back when I was doing these calculations, I was primarily working with traditional boats and props in deadwood/rudder apertures that tend to severely restrict prop diameter.

Idle speed is an issue. My idle speed is now 4 knots and it's a bit of a pain since I often have to shift in and out to creep around anchorages and wait for bridges. It's a good trade off for better fuel economy and an engine that, by its sound, is running better. I can see though why builders wouldn't want to turn the general public loose in boats with that pitch.

My 2QM is nearly twice the weight of the Yanmars that replace it now and intended to run at a lower RPM. It's more tractor than automotive in character. I do have a sooty transom but I did before as well. The rate of soot build up hasn't increased significantly, decreased if anything, but it looks pretty dingy now after over 3000 miles, probably 80% under power.

I'm running a two blade wheel. With the boat clean and light I had 2700 RPM free running which is just 100 under the intermittent maximum so very close to the standard you quote. +- 50 is what reps have always demanded on sea trials in my research vessel designs.

My maximum operating RPM, except when running hard briefly to blow out the exhaust elbow, is 100 over continuous so, if the governor had been reset to commercial standards, I would be slightly under propped. Loaded for the cruising I am doing now and a fairly clean bottom (amazing how well bottom paint works when you run every day), I hit exactly the 2600 continuous RPM. I never see any black or even dark grey smoke. On a warm and dry day, I can run at 2400 and see virtually no visible smoke.

Inlet air restriction is an under considered issue. On commercial boat sea trials, it was always the things the reps were most concerned about. They would have manometers set up in the engine room to measure pressure drop due to the engine sucking air. A hair over the line and they would not approve the installation. I remember on shipyard turning a boat in the slip before dock trials so that the superstructure air intakes would not be facing downwind so that airflow was sucking air out of the engine room. Exhaust back pressure was the next thing they worried about most.

With typical sailboat exhausts (who ever measures back pressure on a wet exhaust?) and situations like my friends oil clogged air intake screen (check for oil in your foam air filter if you have one), I suspect that these fuel mixture effecting factors may contribute significantly to elbow clogging in many cases.

Maine Sail · Dec 28, 2011

Roger Long said:
Inlet air restriction is an under considered issue. On commercial boat sea trials, it was always the things the reps were most concerned about. They would have manometers set up in the engine room to measure pressure drop due to the engine sucking air. A hair over the line and they would not approve the installation. I remember on shipyard turning a boat in the slip before dock trials so that the superstructure air intakes would not be facing downwind so that airflow was sucking air out of the engine room. Exhaust back pressure was the next thing they worried about most.

With typical sailboat exhausts (who ever measures back pressure on a wet exhaust?) and situations like my friends oil clogged air intake screen (check for oil in your foam air filter if you have one), I suspect that these fuel mixture effecting factors may contribute significantly to elbow clogging in many cases.

Spot on. Inlet air restrictions can also lead to plugged elbows and owners who constantly run the blower can exacerbate this, if the engine bay is tight. Ideally the engine bays should have an inlet and outlet if you plan to run the bilge blower and an inlet should be there regardless.

Many a DIY have sealed their engine compartment up drum tight only to run into "engine problems". On our Catalina 310, it had a tight bay, I used the draft gauge from my Bacarach Combustion Analyzer Kit. On the engine compartment at 80% throttle, after a half hour of running, and there was no negative pressure however when I kicked on the bilge blower it went to -.2 meaning the engine was being starved of air. Simple fix on that boat was just not use the blower....

redhead78 · Dec 28, 2011

my mixing elbow

my engine has around 325 hrs, and so far no soot and runs great. I have the high rise ss elbow, I will probably check it out next year. So far ok.....Red

Warren Milberg · Dec 29, 2011

Based on a database of one, my '86 Yanmar 2GM20F shows no signs of coking/carbon buildup/smoking exhaust, ad infinitum, in the 8 years of owned the boat. While this engine can still reach its maximum rated rpms (3400), I hardly ever run it anywhere near that or even to the so-called "common wisdom" 80-90 per cent of that. Perhaps my experience is close to that described by Bill Roosa, that is, running the engine hard is but one part of a complex issue in avoiding elbow clogging (and a variety of other engine problems). I believe that other very important factors include: (1) changing the primary and secondary filters before they really need it; (2) running the engine to recommended operating temperature; (3) avoiding as much idling as possible; and perhaps most important of all (4) using the best quality of fuel with the right cetane rating for your engine (or adding a booster) and filtering any fuel going into your tank to remove water/crud.

Roger Long · Dec 29, 2011

Actually, I don't think my transom looks too bad. This is after about 500 hours of engine operation. The shadow makes it look a bit worse than it actually is. The outlet is under "Maine".

There is a bit more soot under the counter because the quarter wave comes up and puts the outlet under much of the time.

Mixing Elbow

.

.

.

Attachments

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Attachments

.

.