Back in the 1970’s I became heavily involved in the mechanics of boats and before I knew it they became my passion. I have been lucky to have gained over 25 years of experience and 10’s of thousands of engine operational hours (300+ diesel engine installs) and have learned (sometimes the hard way) what it takes to make a reliable engine / power train system, and all that that incorporates. The Marine Exhaust System is a major part of this.
My hopes are that the information in this article will shed some new light on the understanding (and misunderstanding) of one of the most important aspects of a successful boating experience: The Marine Exhaust System.
An important goal here is to remove some of the mystery surrounding much of the misguided and ill conceived “couch engineering” designs that have been imbedded in the boating industry for far too long. Some common sense is the first part that is needed to design a safe and reliable exhaust set up. And, the key word here is “GRAVITY.” Just putting some thought into the general placement of your exhaust system, and with the knowledge that I hope you glean from this article, should help solve many, many horror scenarios down the road. Also remember this (something you can take to the bank), doing it right the first time will leave your wallet much more in tact in the years that follow.
It has been a few years since I posted some thoughts, pictures and politics on Marine Exhaust Systems, so it is time to update. And, since exhaust system design, fabrication, and installation have become a large part of our business, the time is here to share some of what we have learned over the past two decades in this ever changing business.
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The two most basic issues that need to be understood and accomplished:
To this very day, much of our work still involves replacing, rebuilding, or repairing engines solely because of a poorly designed and/or fabricated wet exhaust system that allowed salt water into an engine’s internal workings. Seems the most basic of all natural forces in our lives, “GRAVITY,” was “left out” of the design process, and then, mixing that with couch engineering and “back yard designers,” you now have a recipe for disaster someplace down the road, sometimes very soon after you purchase a new boat.
Let’s start our main discussions with exhaust sizes (NOT overall design, as we must first figure out what is required to meet engine requirements), dissect them a touch, and then decide what is needed and what will work. You must also understand that when we talk “marine exhaust” we are usually talking a “wet” system, but also realize that inside this “wet system” we have two distinct parts. In most exhaust systems that are in the type of boats discussed in these forums (150-800 HP diesel engines), there are TWO distinct parts of the exhaust system/piping. The DRY part and the WET part. Even on the factory supplied 90 degree “wet elbow,” these two sections exist, though many people don’t realize it.
The inner pipe of this “wet elbow” is actually/usually a 90-degree dry bend, or section, surrounded by raw water to keep the surface cool. At the end of this “wet” elbow, where the exhaust hose attaches, is where the water is introduced (hence the term “mixing elbow”) and the exhaust NOW becomes wet. Inside this elbow is a smaller diameter (typically around 2 ½ – 6″ ID) which is the dry side, and where the hose attaches (it expands to (or is surrounded by) 4-10″ tubing/OD piping, depending on the engine size, etc.)
EXHAUST SIZE can be determined by a few rules, but all really come down to two things:
#1 – Meeting the engine requirements as to total restriction (back pressure).
#2 – Designing a system that will FIT inside the boat’s constraints.
Most Important Point to Understand:
Very simple, if you can’t meet Rule #1 and Rule #2, then nothing else matters and the exhaust is the WRONG SIZE. One, it won’t meet engine specifications / requirements, and two, it won’t fit within the constraints of the boat.
As to meeting engine/manufacturers’ requirements regarding “back pressure,” this is where it is so vital to select the correct sizes of piping & mufflers, design the actual layout or flow path, and then put it all together so exhaust flow is not allowed to build up over this maximum pressure limit assuring safety in all aspects related to the installation.
Exhaust back pressure measurements are a very low number, something like what it takes to blow up a balloon. The pressure is usually measured in units of Water Column Height or Mercury (Hg). Typical maximum limits are from 1.5″ Hg to 3″ Hg or 20″ to 40″ of water (right around 1 PSI), depending upon the manufacturer. John Deere, Lugger and Detroit seem to want back pressure lower (about 30″ water max) than Cummins or Yanmar (40″ to 50″ water), and this makes it even tougher to meet the requirements and build a system that will fit. A new specification for exhaust back pressure limit from Cummins for the QSB was just released that will easily allow a well designed 5″ WET system to meet back pressure requirements on the QSB 380 and possibly even the newest 480 version if a well thought out design is used. Cummins now allows 5″ Hg (about 2.45 PSI-68″ of water column) on all the QSB’s. This is a very friendly spec and can make for a much easier and less expensive exhaust system installation.
But, back to sizing. Exhaust flow is determined from the amount of HP the engine makes and the more HP, the more exhaust flow; therefore it will take larger piping and/or less bends, shorter lengths etc., to meet back pressure requirements. Also, a very simple to understand concept (even though most installers seem to forget) is the “bend” equation part of planning an exhaust. Figure a smooth radius 90 degree bend is equal to about 6-10 FT of DRY piping and 15 FT of wet piping. Another good rule of thumb to remember is for every 100 PRODUCED horsepower, the engine makes about 200 CFM of exhaust gases, but this does not include the water and / or steam that becomes part of the mix when water is introduced. That’s why dry piping can be smaller than wet piping, WATER and steam add to the total flow in a substantial manner; therefore once water is introduced, the piping MUST BE LARGER.
Past experience as to what size will work and meet requirements is always a plus when in the initial planning. But not all are so lucky, so they turn to the engine specs or installation guide and see what is “recommended,” and/or they use the factory supplied wet elbow size to go by. In some cases this is fine and gets you by with the least amount of cost and effort. In most cases, the hose size that fits the factory elbows will work in 90% or more of the applications out there.
Below are some notes on 3 most common WET exhaust sizes that have shown to meet all restriction requirements for Cummins engines over the last 20 years and are based upon well over 300 Installation Reviews and exhaust tests. Keep in mind that the dry section and wet section are different and must be treated so. Also take into consideration the type of muffler, the overall length of the system, the amount of both dry and wet bends, the amount of water that you inject into the system (some of it, if not all of it), the angle of the discharge AFTER you inject water and how the system exits the vessel. All of these affect the total system back pressure. I am using Cummins engines as that is what most of my experience is with and I am using 3″ Hg or 41″ of water column as the maximum back pressure limit:
For this discussion, pipe size is always shown as a nominal size in SCH 10 wall ( .120″-ish) – I.E.
“Wet” size is always the actual ID of the exhaust hose. Tube is always the actual OD of the tube (pipe) and is usually about 1/8″ wall meaning a 5″ WET tube or FRP (fiberglass) exhaust tube or pipe has approx a 4 ¾” ID.
Exhaust hose (any hose for that matter) is always sized as an ID measurement and always is sized to FIT OVER a tube OD dimension or pipe outer diameter measurement.
4″ Tube, 4″ pipe size ( 4.5″ OD) & 5″ WET SYSTEMS – 6BT 210, early 6BTA’s – ( 200-250 HP) Factory recommendation is 5″ WET (Yanmar 6YLA too), or most any diesel in between 180 and 250 HP.
Experience has shown that 2.5″ pipe (2.875 OD) for a short length or one “90,” OR 3″ pipe size ( 2-3 90’s) for the dry section, and 4″ tube to 4″ pipe for the wet section and wet muffler is usually fine. This would also apply to a 4LHA 240 Yanmar and 6LPA 315.
6″ WET SYSTEMS – 6BTA’s – 300 ~ 370 Diamonds and QSB’s thru 480’s, QSC’s , QSL’s ( 300-500 HP) – Factory recommendation is 6″ wet.
Well, this is where we have some “fudge factor” if you want to design it right and make it “fit” the boat. Going from a 5″ wet to a 6″ wet ( typically in 300-450+ HP engines ) is HUGE and opens many install capabilities. We like 6″ mufflers and piping from the typical engine room bulkhead aft to the exit near or at the stern. But we like to do our engine risers/custom elbows and wet mixers in 4″ pipe for the dry section and 5″ WET outlets where space is an issue. Using a properly designed dry riser w/ a 5″ mixing elbow, and then transitioning to 6″ at the engine room bulkhead, saves valuable space in smaller engine rooms, saves money for the customer, and is just about always easier and a better overall and “politically cleaner” install. The transition from 5″ to 6″ wet is always easy as 5″ to 6″ FRP tube is an easy make for a custom elbow of any degree at 45 or less. If a highly restrictive muffler is used, or the available space allows the use of 6″ close to the engine, then a 6″ mixer might be the best choice.
8″ WET SYSTEMS – Some “C” & QSC installs, QSM’s-400++ to 800-ish HP-Cummins has “recommended” both 6″ and 8″ and seems wishy-washy on this.
Well, I have yet to see a C, QSC, QSM, or any Cummins (or other make) engine UNDER 500 HP need an 8″ wet exhaust system to meet specs. But, I continue to see this as a RECOMMENDATION for the exhaust size in many cases. I guess if you have the room, the budget, and have an extraordinary amount of bends and/or an overly restrictive muffler, then maybe you should go for it. But from a vast amount of experience, we always stay with 6″ max if under 500 HP.
When we get up into the 500 – 800 HP-ish HP range, this is when we need to think about some, or all, of our WET side of the system being 8″. Since most of my work and the discussions on this site center around repowers of sportfishing boats like Bertrams, Vikings, Hatteras, etc, let’s confine the 8″ to this general style of boat in the 40-60 ft length range. And, with so many older Detroit powered boats/owners still out there that are now seriously looking at repowers, and most of these having 8-71’s , 6-92’s, 8-92’s, etc., this is now even more important to understand.
Usually, these boats have 8″ or even 10″ WET systems aft of the engine room. This is typically where the mufflers are located too. If all is good aft of the engine room – all piping, mufflers, outlets and hoses – (it is usually not), then this is a good size to start with for adapting to the newer 4-stroke engine. If some or most of this piping needs to be replaced because of age, it’s usually easier just to stay with the same size for the section aft of the engine room. If you’d like to size down for space or cost reasons, then a good look at the overall system and engine requirements will be needed.
Let’s look at a new QSM at 670 HP as to what will easily meet the spec. The factory supplies an 8″ fabricated wet elbow or mixer and IMO is of questionable use or quality. Yes, they do work in many applications when used correctly, but also seem to be subject to both internal and external leaks before their time because of the many welds and thin wall construction. Even worse, though, are the “installers” who re-weld or bolt these units in a dangerous “up” orientation in order to build a cheap “Mickey Mouse” type riser. I not only see this with the QSM’s but also in many other installs using the factory 5″ and 6″ “factory” wet elbows.
For those who cannot grasp what the issue is here, a simple explanation – This is a double walled 90 degree wet elbow that was never designed to “hold water” in this orientation but, rather, be mounted horizontally so as to exit downhill and self drain. When installed like this, the sea water that will eventually corrode thru the elbow will now go down the pipe into the turbo or worse. I hope you do not recognize this type of system on your boat!
Now, back to 8″ – This is what we have found with engines in the 600-700 HP range as to designing a wet exhaust system and working around the existing 8″ – 10″ piping or “book” recommendations. We typically use 4″ dry piping from the engine up to a well designed 6″ wet mixer. This usually includes 3 to 4 pieces of 4″ pipe size “weld” 90 degree dry elbows and then a double walled wet mixer of our design orientated on the downhill side of the system. The mixer is always pointed to a spot on the vessel so we DO NOT have to incorporate any WET bends / “90’s”, etc., BEFORE the transition to 8″ (or 10″) from the engine room aft.
With good design and thought, along with some first class fabrication, meeting exhaust restriction requirements can easily be done with a mix of both 4″ dry, 6″ and 8″ wet which will make for a much cleaner install while making the engine room more user friendly as to maintenance, etc.
To recap, exhaust size is something that can be adjusted to not only meet requirements for the engine, but also fit the vessel’s constraints. When sizing the system to meet acceptable restriction requirements in order to protect the engine from excessive back pressure, keep bends to a minimum, especially “wet” 90 degree bends. With some planning, most exhaust routing designs can eliminate a one or two 90 degree bends by building a custom riser/mixer and make for a less restrictive, less cumbersome and safer exhaust system.
In closing, please understand that with some good engineering and thought, a well designed exhaust system can make a big difference in the layout of the engine room and offer a superior design as to safety and functionality. The idea that rarely a month goes by without our shop seeing a disaster from water ruining an engine from a “factory” type exhaust system or from an OEM builder with his head between his legs still befuddles me. To this day I see drawings from architects who have no clue. The drawing below is from a boat being built that is just such – All that height in the engine room and the architect has the system riser backwards – Just ask yourself what would happen while cranking the engine when out of fuel. And just as bad is that he got paid to design it this way. Sad, very sad…….
Marine Exhaust systems are one of the more important construction features on a vessel. Done wrong they are not only a safety issue for the passengers and the vessel, they can also lead to premature engine failure and / or indirectly cause poor maintenance to be performed on a vessel because of lack of design thought in the engine room. So many times when the exhaust design is an “afterthought,” normal or routine maintenance is close to impossible.
If you give this some thought in the future, maybe this will help you in your next repower or new boat design – The energy that a typical 400 Hp diesel puts into the propeller is matched close to 100% by the energy that goes out the exhaust system. So if you think your power train needs to be well designed, don’t cut any corners on the exhaust design – It needs to be just as tough and built with the same degree of design to handle that kind of energy.
Hopefully the pictures and design ideas incorporated here will help remove some of the mystery in exhaust design that seems to elude much of the industry. I fully understand that a buyer of a new boat does not have much input as to exhaust design when purchasing a new or used vessel, but we hope the guidelines here help not only the buyer to understand what to look for in a boat, but also will prove to be beneficial to the builders in the design and planning phase of marine engine rooms.
Designing a marine exhaust system for a boat is something that apparently takes the back seat during the planning stages when doing a repower. In new boat construction, the design of many systems seems to center around the “cookie cutter” philosophy, as builders always seem to want to or work around a factory designed wet elbow system that is supposed to “fit all”. Besides that, many new builders are more concerned about getting the engine below a low deck than worrying about the exhaust and exhaust outlet of the engine being close, at, or BELOW the water line.
Also, and another all too common error in exhaust design, is the use of an anti-siphon valve as a “fix-all” for an otherwise poor and sure to fail design. It’s not that an anti-siphon valve is not needed in many applications, but “Average Joe” has no clue as to what they can do and more important, what they CANNOT do, and how small changes in the basic design of an anti-siphon valve can greatly enhance its effectiveness. More on “Anti-Siphon” valves and their shortcomings below.
The most BASIC of all supposedly understood but not followed diagrams of a marine exhaust layout is below. Why is it we continually see the LWL of a vessel within just a few inches of the exhaust spill-over point? Notice the word MINIMUM??
The diagram above seems to elude new boat designers and “repower experts” in so many designs that have cost vessel owners millions of dollars over the years in ruined engines. Simply unbelievable to me that something as simple as building an exhaust with a minimum of 12″ of safety margin height is not followed.
Moving on to the total design of the system is where most of the emphasis needs to be when repowering or building a boat. With “design” we mean the entire system from the engine exit point (the turbo outlet in most cases) all the way to where the exhaust leaves the boat. This includes the “size(s)” (just figured that one out), from the engine to the final exit, type of muffler, if any, type of material for both the dry and wet side of the system, and the general routing and actual installation of the system. It seems that many installers and builders plan this very important part of the vessel as an “afterthought” because many great engine rooms are built with no room remaining to build a safe and well planned exhaust system.
Material choices when building exhaust systems can vary, but 25+ years of experience and 100’s of exhaust systems under our belt in high hour commercial applications have shown us that 304L or 316L is good for all of the dry sections and shows no difference in lasting ability regardless of what “street talk” says. Using 316L for all wet sections is always best. Use 316L rod for all welding (304 or 316) and if the design uses any mild steel for the dry section, then use 309L for the mixed joints / weld area. TIG is the method of choice for all welding. For all custom FRP exhaust work, the of use resins that are Class 1 fire retardant isophthalic polyester resins are our choice and easy to source. Common industry names are Reichhold (DION) and McNichols and are used extensively thru the FRP structural pultrusion process and filament winding manufacturing industry. You may also find many of the more common iso-tooling resins meet these specs and are also an excellent choice to use, although some do not have the Class 1 rating. IMO, 99% of the time, Class 1 resins are not needed unless the spec calls for it.
Resin rich lay-ups are best with plenty of thickness ( ¼” to ½”) in all joints building up with glass-strand mat with a layer or two stitched fabric in-between. We finish with iso-gel coat and surfacing agent when applicable / paint as to what looks right for the job – in all cases our work is always vastly more stout than “factory supplied” FRP parts, and we always put a 2″ – 4″ long tube doubler inside all tubes where the hose clamps go. This eliminates the tube crushing that factory pipes/ muffler spigots seem to be very susceptible to.
With sizing and basic construction covered, let’s get into exhaust design, as this is the most abused and least understood phase of the overall system. “Gravity,” I’ll say it again, “G-R-A-V-I-T-Y,” is the most important aspect of the design that needs to be addressed and how you can use that force to help you design a safe and effective exhaust system. Next is understanding and knowing where your waterline is in both static and all running conditions.
With those ideas fresh in your mind these are some pointers and concepts that you need to consider in the initial planning stages of the design layout:
From the engine manufacturer regarding exhaust design. They may “require” a minimum specified exhaust height for safety, but “recommend” a particular size for the system based on past experience. Many times smaller exhaust sizes can be used to everyone’s advantage and employing an experienced company w/ hands-on experience for this part of the vessel construction or repower is time and $$ well spent.
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Water flows downhill so, if you have a system that holds water (water jacketed risers for instance) and this system fails internally (it’s not IF it is going to fail, it’s WHEN it will fail), where will the water go?? Into the turbo/exhaust manifold/cylinders?? Think about YOUR riser or elbow should it fail internally where you can not see it and what might happen. Remember, WET risers are an absolute no-no for any long term application unless they are “coolant cooled.” Internal failure of “wet elbows” and custom water jacketed risers is an old and ongoing problem, regardless of material choice and/or other claimed construction features. (See Tip #7).
For the riser (where needed and is practical) BEFORE turning over the top and injecting water; i.e. always inject the water on the downhill side, or down stream of the top of the riser. A wet exhaust system with a steep downward slope is always better and safer. The cheap way out, by using a factory supplied “cookie cutter” designed wet elbow, is not always a good or safe option. When thinking marine exhaust, remember “one size” DOES NOT FIT ALL.
Although this can’t always be done, you can still build a safe system by utilizing other simple design ideas, custom mufflers, surge tubes, etc. An important point to remember, IF your muffler, etc., holds water in the static position, then the system is also holding water when lifting/pulling the boat at the yard. ALWAYS lift the bow first (noticeably bow high) and hold it there for a minute or so to let the water drain from the system. I have seen quite a few destroyed engines that had water slosh up into the cylinders from this exact scenario of water rolling back and forth or lifting the stern first when pulling a boat – Usually this is not discovered until launch time and by then the engine is toast.
By being sure that the engine “spill-over” height is higher than the lift muffler spill over point. When the water injection is below the water line, you can also design an “active” anti-siphon valve that is much safer than the typical “auto-type valve” shown or used in most applications (IMO, they are a poor design and should be avoided unless fully understood as to their shortcomings and checked for proper operation on a continuous basis ).
Some of the fallacies that still persist today are shown in the “copied” lift-muffler design below that is shown in current high dollar color catalogs touting their exhaust muffler products. Thinking that this is an applicable base type design for a lift muffler system is 100% hogwash and in many cases leads to ruining a perfectly good engine because of water rising within the system before the engine starts and after it is shut down. What they should be saying is to design a riser BEFORE the water injection to use all of the height available within the engine room, and to design an anti-siphon system that allows an active and “open” siphon break to be on the upward rise of the water injection system allowing water to flow over the side BEFORE the water flows into the lift muffler filling the system.
Again, another instance of 100% “couch engineering” from an engineer that has probably never done and/or seen an install of a marine engine at or below the waterline and only gives or sells his “expertise” based on theoretical circumstances on paper calculations. This kind of literature angers me as I know it’s total garbage. However, I do admit that when this type of engineering is taken for “gospel,” I make lots of $$ because it assures me of continuous new engines sales down the road.
The general layout of the “anti-siphon” valve. In reality, it’s not a valve at all, but an active bypass that should be installed on the uphill water flow before it goes over the top, and discharged over the side above the waterline in a VISIBLE location. This allows cranking without flooding the lift muffler and adds an enormous layer of safety to the system.
Typically, many use factory 90 degree wet elbows, and an array of 45 and 90 degree bend hoses and clamps routing an exhaust. I guess most installers think of a marine exhaust system like copper plumbing in a house.
A simple change from a 90 degree angle bend to a 75 degree bend, an angled input to a muffler, or an added twist in a riser can make a world of difference in overall exhaust layout. In other words, don’t just think “straight, 45 & 90” when designing an exhaust system. In the 100’s of exhaust systems we have designed over the last 25+ years, I am sure that at least 50% of them had to have something custom done to a “factory muffler” in order to make the exhaust layout “fit” design criteria.
An Interesting Note: I have tested the pressure drop of a typical 75 degree custom elbow from both 6″ to 8″ and 5″ to 6″. In both cases, at 430 HP on the 5-6″ elbow, and at 660Hp on a 6″ to 8″ elbow, I never saw more than ¼” Hg delta. Going from smaller to larger allows a quick expansion and lowers pressure restriction overall even in relatively sharp wet bends. Less bend would even be better.
It is not IF they are going to leak, it’s when they are going to leak as it is a 100% given that they will. If this is the only viable option, then be sure that you realize that they need to be inspected annually (or more often), or changed out after every few years to be safe. A few examples below of perfectly good low hour engines that had a “wet riser” or something similar and when they failed internally, the owner was into the BIG bucks as to repair.
(like installing a muffler in a confined space) and you need to reduce back pressure but you cannot install larger pipes, tubes, etc, another option would be to bypass some of the water that is normally mixed into the wet exhaust.
In most cases, the engine seawater system pumps more than enough water to cool the engine and sometimes as much as 2+ times water than needed to cool the exhaust.
This can vary as to engine design AND exhaust design, but bypassing approx 1/3 of the water that leaves the heat-exchanger or cooling system on the engine and sending it over the side of the boat can easily reduce back pressure by 1″ Hg or more in some cases.
An added benefit of this is that it can add a “visual” as to water flow and, in many boats, this would be a plus as the seawater water flow is sometimes impossible to determine.
Knowing that you are pumping seawater always adds comfort to your experience. If this is something that you feel would be needed, use the services of a company that has a track record in this type of work as it would be time and effort well spent.
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The boat was sold here locally and on the first trip out to the islands in “prevailing weather,” while fishing with the engine off and the boat bobbing up and down, both engines had the aft cylinders fill with salt water. Luckily the captain called me and I told him what he had to do to salvage the engines. That night after a long tow back to the dock, we pulled the injectors and flushed the cylinders out. The next month was spent re-doing the exhaust system (about a $12K job).
The stock riser was about 2″ above flooding when brand new and within the first year, as the vessel got loaded with “gingerbread,” the engine flooded at the dock. The engine was toast and the owner had to buy a complete NEW engine.
These pictures show what is “typical” marine type couch engineering mixed with FACTORY salt water cooled wet risers that were installed on a 3126 CAT. The factory risers were made of Stainless Steel with the salt water inlet at the bottom of the riser. Two things happened over 4 years and 190 hours. Because the riser outlet at the top were designed and installed at such a “shallow down angle” (have seen this on new Mainships too), water would drip down the riser during cranking and after shut down damaging the turbo. After about 3 1/2 years/200 hours in service, the riser failed internally leading to total failure of the turbo and failure of the #6 cylinder exhaust valve. CAT later changed from Stainless Steel to Bronze construction for this design (that solved the “rotting out internally part” of this poor design) only to have the shallow angle of the outlet come back and bite them on many Mainship installs. It took CAT engineers about 7-8 years to understand the issue (gravity being the main culprit) and they finally dumped the entire design with the last generation of 3126 CAT’s and the newer C-7’s.
If you recognize this design of a wet elbow on your boats exhaust system, I’d be checking the internal condition of it often after the first 3 or 4 years of “marine age”, regardless of total engine hours….
Original builders design and installation: Results of very poor design and “Mickey Mouse” exhaust wraps. On the maiden voyage and seatrial, engine room ceiling tile caught on fire.
Our Solution: A re-designed riser and mixer, proper clearances and supports, and 1st Class Exhaust Insulation on the dry sections. In the big scheme of things, this could have been an expensive learning curve. Guess who’s wallet picked up the $6500 “redo” tab? Just like most of the time, the owner !!
This is a Volvo Factory supplied wet mixer for a newer Volvo TAMD 120. At 800 hours and 4 years the owner was complaining about black smoke. We pulled the air cleaner and found the turbo was binding.. Noticed external water leaks on the factory supplied exhaust mixer and pulled it. The inside was also leaking and some rust was apparent on the exhaust turbine wheel w/ lots of crusty carbon/salt build up.. Cleaned it all up and installed a new “factory elbow” at the tune of $2800 each – he did not want a custom unit. The overall design, multiple pieces, and internal seams and welds says it all. Very poor design and he is sure to see the same failure again as the new elbow was of the same construction. In my opinion, the owner got off easy as it could have been a lot worse.
These picture’s are a perfect example of a design that may impress a buyer but shows a total lack of thought as to both raw water flow, dry riser design, and long term reliability and safety for the engine because of the “jacketed design” and orientation. Not only does the raw water input elbow go against any common sense as to water flow restriction, with the overall design with internal welds in the jacketed area, this elbow will fail and leak into the turbo when it does rot out internally (just a few years down the road at best). The supplier (a well respected popular engine distributor) should not be in this part of the business, or at least use a different company to design and build the exhaust mixers and risers. The first pair of supplied units were recalled for possible cracked welds. Just another sad example of “couch engineering”.
The designer/fabricator tried his best to make a buck – This riser was on a Detroit 650 HP 8V-92 and failed in two ways – The exhaust sprayer (inside pic) was clogging and the engine would either overheat or the raw water hose would burst – One time the burst hose took out a new Inverter. Then, after dealing with that issue (working with another local mechanic that had no clue) the unit failed internally and took out the turbo. About $10,000 later we finally got it fixed right. Moral of the story: Never never do you want a raw water jacketed riser!!!
This builder thought for sure you could put the riser/turbo at the waterline, inject water in a jacketed riser that is close to level, and then push it up hill – Within 3 months and less than 25 hours the engine had water in the turbo and cylinders – Actually it probably had water in it the first day, but somehow the engine did survive for a couple of months… What was he thinking!!!
This is another example of a repower job that cost a extra few bucks after someone thought they had it right. The “repower guy” seemed to think that exhaust systems could be plumbled like water pipe in a house and attempted to use the factory “one size fits all” cookie cutter wet elbow. He also forgot about gravity and within 2 weeks had starting problems. The turbo was getting washed daily with salt water… Designing a proper riser the first time around is always cheaper.
These pictures depict what we see quite often with the CATAPILLAR factory wet elbows – Poorly designed wet mixers that “clog” unnecessarily due to a “couch engineered” design…With all the issues we have seen with the different type of CAT Factory wet risers and mixers, I really wonder where they hire their engineers from.
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