Since I was bored last week with nothing to do with my spare time, I decided to do some "routine maintenance" on my boat. I removed the mixing elbow for inspection and cleaning by first unbolting it from the engine and removing the hose. At first it looked like it could use some cleaning from where I could see, but after separating the three pieces (elbow, nipple, and U shape piece?)I couldn't believe my eyes. The two inch diameter opening was clogged down to no more than half an inch!! Cannot understand how the engine was still able to run without any noticeable loss of power. I can't wait to see how the engine will run in the spring with the new mixing elbow. The boat in a 1997 so for all of you who think that the mixing elbow is a "no maintenance" item, think again. And in order to separate the elbow from the nipple with the opposing threats, be prepared to put it in a large vice and use an iron pipe at least three feet long for leverage. S/V Calaloo
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Typically 3-5 years disposable item.
Lee: The mixing elbow is typically a 3-5 year disposable replacement item when used in salt water. They will last almost indefinetly when operated in fresh water. It is good to operate your engine at it optimum operating range 70-80% of Max. operating RPM. Most of the newer Yanmars are rated at 3600 max. Running at lower speeds encourages additional build up of the elbow and glazing of the engine cylinders.
Lee: The mixing elbow is typically a 3-5 year disposable replacement item when used in salt water. They will last almost indefinetly when operated in fresh water. It is good to operate your engine at it optimum operating range 70-80% of Max. operating RPM. Most of the newer Yanmars are rated at 3600 max. Running at lower speeds encourages additional build up of the elbow and glazing of the engine cylinders.
Lee, please describe your engine usage
Do you use your engine very little? How many hours on the unit? When used do you run the engine at 80% of WOT? I have a Volvo in my 1997 h40.5 and I have inspected the elbow about 3 years ago and found it to be very clean. In fact there were no deposits to clean out- just a light coating of carbon. I always run the engine at 2200-2500 rpm. WOT is 3000rpm, so 2400 is the 80% point for me. I run in salt water. I normally use the engine for at least an hour at a time. I'm wondering if I am not a typical user and if for engines that get much lighter use heavy carbon deposits are much more likely.
Do you use your engine very little? How many hours on the unit? When used do you run the engine at 80% of WOT? I have a Volvo in my 1997 h40.5 and I have inspected the elbow about 3 years ago and found it to be very clean. In fact there were no deposits to clean out- just a light coating of carbon. I always run the engine at 2200-2500 rpm. WOT is 3000rpm, so 2400 is the 80% point for me. I run in salt water. I normally use the engine for at least an hour at a time. I'm wondering if I am not a typical user and if for engines that get much lighter use heavy carbon deposits are much more likely.
Mixing elbow is
the cast iron part at the output of the exhaust manifold which serves to mix water into the exhaust gas to cool it before it passes into the rubber exhaust hose.
the cast iron part at the output of the exhaust manifold which serves to mix water into the exhaust gas to cool it before it passes into the rubber exhaust hose.
Home depot model design
It is made of 1 1/2 inch black pipe fittings. Street ell goes into the manifold. Close nipple into that. Tee (middle hole) onto that. 6 inch nipple goes onto the bottom of the tee and that connects to the exhaust hose. Top hole of the tee is where you put a 1 1/2 inch to 1/2 inch double tapped bushing. Ask a plumbing supply store for that. Home depot won't have it. Adapt the top side of that bushing to the water hose which used to go to the old elbow. On the inside (lower side) of the bushing, you will need to attach a 6 inch X 1/2 inch nipple. Before you install that nipple, make a dozen small holes (1/8 inch or so) around the lower half of that nipple. Make sure the holes are below the middle opening of the tee. These holes are where the cooling water gets squirted into the exhaust gas. You do not want cooling water going back into the manifold. You also need to cap (or tap and plug) the lower end of that pipe. Parts cost about $20. Seal everything with high temp antiseize compound. Do not use teflon tape for this application. It makes a toxic gas which can be lethal as I am told. Do not over tighten anything and it will come apart much easier later. I got two of everything when I made mine so I will have a replacement for anything that fails. It is still ok after two years and I check it when I change oil. I wrapped some fiberglass tape around mine just so that I could not accidentally touch the hot parts of this thing. It gets much hotter than the stock part so it may produce more heat in your engine compartment too.
It is made of 1 1/2 inch black pipe fittings. Street ell goes into the manifold. Close nipple into that. Tee (middle hole) onto that. 6 inch nipple goes onto the bottom of the tee and that connects to the exhaust hose. Top hole of the tee is where you put a 1 1/2 inch to 1/2 inch double tapped bushing. Ask a plumbing supply store for that. Home depot won't have it. Adapt the top side of that bushing to the water hose which used to go to the old elbow. On the inside (lower side) of the bushing, you will need to attach a 6 inch X 1/2 inch nipple. Before you install that nipple, make a dozen small holes (1/8 inch or so) around the lower half of that nipple. Make sure the holes are below the middle opening of the tee. These holes are where the cooling water gets squirted into the exhaust gas. You do not want cooling water going back into the manifold. You also need to cap (or tap and plug) the lower end of that pipe. Parts cost about $20. Seal everything with high temp antiseize compound. Do not use teflon tape for this application. It makes a toxic gas which can be lethal as I am told. Do not over tighten anything and it will come apart much easier later. I got two of everything when I made mine so I will have a replacement for anything that fails. It is still ok after two years and I check it when I change oil. I wrapped some fiberglass tape around mine just so that I could not accidentally touch the hot parts of this thing. It gets much hotter than the stock part so it may produce more heat in your engine compartment too.
Mixing Elbow-Boat Usage
Rich, I use my boat almost every weekend during the season and run it at about 80% WOT if not more. The extend of the blockage could not be seen by removing the elbow assembly in one piece. You have to actually separate the U piece from the nipple since the build-up was on the other side of the U. I could have chipped the build-up away and clean it but decided to go for a new three piece assembly since I got a good price from an outfit in Annapolis. I'm on the Chesapeake Bay so the water is between fresh and salt(brackish). S/V Calaloo
Rich, I use my boat almost every weekend during the season and run it at about 80% WOT if not more. The extend of the blockage could not be seen by removing the elbow assembly in one piece. You have to actually separate the U piece from the nipple since the build-up was on the other side of the U. I could have chipped the build-up away and clean it but decided to go for a new three piece assembly since I got a good price from an outfit in Annapolis. I'm on the Chesapeake Bay so the water is between fresh and salt(brackish). S/V Calaloo
Yanmar parts
Yanmar MSRP on the three parts that make up the exhaust elbow for 2GM and 3GM is $229.12. Then theres the $5.00ish gasket. Pat McCartin Inland Marine Diesel Buford, Ga imd_ga@hotmail.com
Yanmar MSRP on the three parts that make up the exhaust elbow for 2GM and 3GM is $229.12. Then theres the $5.00ish gasket. Pat McCartin Inland Marine Diesel Buford, Ga imd_ga@hotmail.com
One of the chief causes of blockage of the
Injection elbow is 'old fuel'. Diesel fuel only has a 'storage life' of 6-12 months. During that time the lighter fractions of the fuel volitizes out the tank vent, and alphines/parafins, gums, etc/ begin to form in the fuel. These begin to 'particulate' and agglomerate into 'soft' deformable particles (that pass right through filters) that remain unburned in the combustion chamber ..... but DO adhere to the hot exhaust surfaces as 'coke', especially at the water injection port. If you want fewer maintenance headaches with your water injection elbow .... use 'fresh' fuel. Diesel fuel is 'reactive' to copper (boat fuel lines) and other metals which accelerate the degrading process ... and usually needs to have an 'inhibitor additive' to prevent this reaction. The Yanmar dealer in Annapolis is Bayshore Marine ... they are a quite good dealer
Injection elbow is 'old fuel'. Diesel fuel only has a 'storage life' of 6-12 months. During that time the lighter fractions of the fuel volitizes out the tank vent, and alphines/parafins, gums, etc/ begin to form in the fuel. These begin to 'particulate' and agglomerate into 'soft' deformable particles (that pass right through filters) that remain unburned in the combustion chamber ..... but DO adhere to the hot exhaust surfaces as 'coke', especially at the water injection port. If you want fewer maintenance headaches with your water injection elbow .... use 'fresh' fuel. Diesel fuel is 'reactive' to copper (boat fuel lines) and other metals which accelerate the degrading process ... and usually needs to have an 'inhibitor additive' to prevent this reaction. The Yanmar dealer in Annapolis is Bayshore Marine ... they are a quite good dealer
q, 007 here 
I do not subscribe to the "old fuel" theory. It is an interesting and maybe even plausible explanation of the elbow blockage problem. One point you made is that the "particles" adhere to the hot parts of the exhaust system. My experience is that if there are such old particles, they will adhere to the cold parts of the exhaust system not the hot ones. My Home Depot elbow runs much hotter than the stock part and I think that will help keep it open regardless of whether the particles are old or new.
I do not subscribe to the "old fuel" theory. It is an interesting and maybe even plausible explanation of the elbow blockage problem. One point you made is that the "particles" adhere to the hot parts of the exhaust system. My experience is that if there are such old particles, they will adhere to the cold parts of the exhaust system not the hot ones. My Home Depot elbow runs much hotter than the stock part and I think that will help keep it open regardless of whether the particles are old or new.
Patrick, why hotter?
Why does your exhaust run hotter? Is that a good thing? Sounds to me it might indicate a problem. What engine do you have?
Why does your exhaust run hotter? Is that a good thing? Sounds to me it might indicate a problem. What engine do you have?
Richard, 007 here
The stock elbow is a heavy cast iron part with a water jacket on the top. That water cools the casting before it is injected into the exhaust. The casting is also fairly restricted at the place where the exhaust goes into it. Using black pipe fittings reduces the restriction. My engine runs much better without the restriction. There is also no water jacket to cool it and the metal is less weight than the stock elbow. Those factors lead to the top of the tee becoming much hotter than the Yanmar part. I wrap a little fiberglass cloth around it to keep from touching the hot area and also to keep the engine compartment heat down. It has worked fine for a couple of seasons now. I have a 3HM35 engine but many of these Yanmars use a similar elbow. I would recommend that anyone with a Yanmar engine should check and clean the elbow every year and any time the engine starts to put out black smoke under a load. One of the reasons I made my own elbow is that I could not find one when I needed one and it was very hard to disassemble without a shop and a big vise. I got all kinds of prices from suppliers and they were unreasonably expensive. The reverse threaded nipple is also hard to remove or obtain. I could not buy one online because of Yanmars marketing geniuses plan. The pipe fittings are readily available except for the double tapped bushing and they can be easily disassembled if need be. The retail price of all of the common parts is less than $15 and I can get them anyplace where you can buy plumbing parts. I do not need a 3 foot breaker bar and a big vise to take this thing apart and I do not have wait for UPS to arrive at some remote marina to get the parts to fix my engine. I would suggest that anyone with a similar engine at least consider getting the parts for an emergency if they are going far from home. Like I said the only hard to get part is the double tapped bushing. Every other part is readily available just about anywhere.
The stock elbow is a heavy cast iron part with a water jacket on the top. That water cools the casting before it is injected into the exhaust. The casting is also fairly restricted at the place where the exhaust goes into it. Using black pipe fittings reduces the restriction. My engine runs much better without the restriction. There is also no water jacket to cool it and the metal is less weight than the stock elbow. Those factors lead to the top of the tee becoming much hotter than the Yanmar part. I wrap a little fiberglass cloth around it to keep from touching the hot area and also to keep the engine compartment heat down. It has worked fine for a couple of seasons now. I have a 3HM35 engine but many of these Yanmars use a similar elbow. I would recommend that anyone with a Yanmar engine should check and clean the elbow every year and any time the engine starts to put out black smoke under a load. One of the reasons I made my own elbow is that I could not find one when I needed one and it was very hard to disassemble without a shop and a big vise. I got all kinds of prices from suppliers and they were unreasonably expensive. The reverse threaded nipple is also hard to remove or obtain. I could not buy one online because of Yanmars marketing geniuses plan. The pipe fittings are readily available except for the double tapped bushing and they can be easily disassembled if need be. The retail price of all of the common parts is less than $15 and I can get them anyplace where you can buy plumbing parts. I do not need a 3 foot breaker bar and a big vise to take this thing apart and I do not have wait for UPS to arrive at some remote marina to get the parts to fix my engine. I would suggest that anyone with a similar engine at least consider getting the parts for an emergency if they are going far from home. Like I said the only hard to get part is the double tapped bushing. Every other part is readily available just about anywhere.
Patrick
Thanks for the info. The reason I asked is that I made a very similar setup (except I got my stuff at Orchard Supply Hardware, even the bushing and a threaded to hose barb nipple that fit). Mine works great and doesn't run hotter. The old one was hot too! But, I have a Universal and the "stock" elbow just injects the water directly into the exhaust. No cooling jacket. So that's the difference.
Thanks for the info. The reason I asked is that I made a very similar setup (except I got my stuff at Orchard Supply Hardware, even the bushing and a threaded to hose barb nipple that fit). Mine works great and doesn't run hotter. The old one was hot too! But, I have a Universal and the "stock" elbow just injects the water directly into the exhaust. No cooling jacket. So that's the difference.
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