Cummins 150 Exhaust Mixing Elbow

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Commander Ed

Active member
Joined
Jul 16, 2009
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40
Fluid Motion Model
C-248 C
Hull Identification Number
90001
Vessel Name
Sea Dragon
I am in the process of replacing the turbocharger on my Cummins 150. While I have had my boat since 2009, this will be the second replacement of the turbocharger. Since I only have about 350 hours on the engine - this seems to be too often to me. (first replacement was at about 75 hours and was done under warranty with no charge $). I am working with the local Mercury Marine folks (as they have taken over the service on this engine) - and was told that I needed to replace the mixing elbow as well as the 3.5 inch diameter hose that exhausts. I have ordered the elbow, and now am being told that the diameter on both the intake and exhause side is different from the original equipment from the factory. What I want to know - is there a special mixing elbow that was adapted for the Ranger 25? Apparently the hose from the turbo side is "special made" and the exhaust side of the hose is smaller that original equipment. Please let me know as I am hoping to replace without a lot of adaptors and additional expense.
Commander Ed
 
I'm currently replacing a metal connector in my 2008 R25, but I"m not 100% clear on what the "exhaust mixing elbow" is. I would think it's the soda pop sized thing the exhaust hose connects to at the turbo? And "mixing elbow" refers to it mixing some water into the exhaust flow?

The exhaust hose comes from the turbo into about a 90 degree elbow and then across the engine compartment to a grey plastic canister that then exhausts to the outside. The 90 degree elbow is 3" at both ends and then prior to connecting to the grey plastic canister there's an adapter that takes the hose from 3" to 3.5" and that's what I'm replacing. The order form from Ranger Tug lists it as "3" Exhaust Port" and it was $78.60. If you call Richard he should be up on this as he sent me one just last week.
 
That's interesting. The turbo on my R25 was replaced by the prior owner just before I purchased the boat. It is also a low hours engine. Seems like several failures with low hours on them. Has anyone gotten any feedback on the cause of failure? Any indication that it is from water getting into the turbo? I've been a bit concerned about how close the water injection is into the "mixing elbow" relative to the exhaust of the turbo. Salt water and a hot turbo are definitely a bad combination if they find one another.
 
I make it a practice to run my RPM's way up every few hours for about 15 minutes to exercise the turbo and get my engine temperature maxed out. As much as we all like to cruise slowly and smell the roses I think running things up once in a while is good practice. I am not sure if lack of use is a contributing factor to some of these failures. It would be interesting to find out exactly what the failure was with the turbo.
 
I have also seen some turbos replaced on the Cummins engines but not a significant amount. If I jog my memory back, I am pretty sure that we had those elbows specially made for that engine and installation. I don't think salt water is the culprit as the technician doing the repairs would certainly notice that right away. I would recommend contacting Richard in our parts department to see what he might be able to dig up in terms of information on the exhaust elbow. He can be reached at parts@rangertugs.com or by phone at 253-839-5213.

Thank you,

Andrew Custis
 
Thanks to all who have replied. Andrew, I will contact Richard, but unsure what to ask him. I had to order the mixing elbow and turbo from Mercury Marine. While the turbo looked the same, the mixing elbow was very differenct and needed a couple of "adaptors". Maybe I should have contacted Richard for one that was like the one I had???

Bottom line, the turbo is still not performing as it should - performance on the boat is down for WOT RPM (about 3700), and speed only about 15.5 Kts. (half fuel - empty holding tanks and 1 person onboard) I have the Mercury Marine Guys going to hook the computer up on an upcoming sea trial to see if we can find out what is happening. With only about .5 hours on the new turbo - it has become so hot that all the paint has burned off the turbo and the connector to the elbow. In addition it started scorching the cover shield. This is what the old turbo did as well. (as well as the OEM turbo)

I am not wanting to point fingers at this point, but with other people having turbo issues at very low hours - there may be a design flaw. I do tend to cruise at higher RPMs (not WOT) than others as just like "getting there", but I can't afford to replace turbo's and exhaust elbows every 100 hours (avg). I will post again after the Mercury Marine folks do more troubleshooting.
 
Ed, please keep this thread going once the Mercruiser folks finish the sea trial. I think the results may be interesting!

I have had performance issues with our Cummins QSD since I purchased the R25 classic new in 2010 (MY2009). Symptoms somewhat the same as what you are describing, lower than rated RPM at WOT (3650-3750 vs 4000) and speed around 16kts. One reading which I watched closely was boost pressure as at WOT boost was reading 16.2 - 16.5 (performance spec 17.40 - 20.30). My first thought was weight as this is our home from May-October and then stored for winter. Pulled prop and had pitch reduced from 15 to 14. No change. This past winter I had the prop tuned by computer scan which showed I should be at 13.2 pitch. Post winter shakedown last week and a first - WOT reached 4,050 which is gov limit (one person, 55gals fuel, no water and holding tank empty). Speed managed 17kts+/-. The interesting part was boost still reading 16psi.

Since we have owned the tug I have been concerned the turbo is getting hotter than it should, paint burned off, melted spot on engine cover and black soot. The soot I thought okay, gaskets which might mean a small exhaust leak at the turbo thus maybe contributing to low boost. Replaced mounting gaskets, no change. I am by no means a turbo expert nor a statics guy but if there have been a handful of turbos fail on the population of Cummins-Mercruiser engines in our tugs is something driving this? Therefore, please give us feedback from the sea trial.
 
Just Dreamin
Interesting symptoms that you are experiencing - similar to mine. Soot was the first indications that got the Cummins Rep to replace my first turbo at 75 hours. It was really apparent. There was less soot on my second turbo that was just replaced, but far more indications of overheat. Now with this third turbo - in only 30 min - it is obviously too hot. Will get my sea trial with Mercury Marine on Friday and I will post then.

BTW - at zero load (prop not engaged) the WOT is always 4050. It is important to record the throttle position and load as well as your turbo PSI. My load was 99% and still getting only 3700 RPM. It is curious / confounding / and just plain disappointing. When my boat was new - first turbo - it was not unusual to see 4000 RPM and 20+ knots. I though I might have a hull or prop issue, but just had haulout and all is good. Fresh bottom paint and clean prop. So I know those are not issues.
 
You might investigate boatdiesel.com. there is a ton of info there on different engines and problems. It is however a subscription web site.
 
Ed, same indicators. Prior to this last prop tune I could reach 4,050 at the dock with no problem. On the water, fairly constant 3650 to 3700 at 100% throttle and 99% load indicating on the Smartcraft, boost ~ 16.2 - 16.5 with speed average of around 16 kts. I never reached 4,000 on the water until this last prop tune where the pitch was reduced to 13.2. Touched 4.050 but still had a low boost (16psi). Did not have an opportunity to check throttle and load percent. I know those reading were next screen over but weather was becoming a factor. I understand turbos run extremely hot but not to the point where they should melt the cover and leave exhaust soot on the heat blanket and turbo mounting locations. And, with all the exhaust leakage indicators on the turbo I feel this is or one of the factors involved in low boost. Would be nice, since these are Cummins branded engines, if our turbos were Holset.
I am happy the prop tune brought my RPM up and hopefully it will stay up as summer weight is added. However, the turbo is still lingering out there and still trying to understand the low boost pressure. Looking forward to your report back from Mercruiser technicians.
 
When I started watching this thread I was worried about turbo failures associated with low rpm operation. But it seems like one thing these failures have in common is running the engine at the other end. From what I know the previous owner of my boat wasn't fond of going slow. I feel a lot better about the prospects in my own situation but can feel your pain.

What kind of indicated load are you guys showing at typical cruise speed?
 
Dan,
Unfortunately all of my recorded data is on the tug and I will not be back up there until later in the week. Therefore, can not answer your question on loads, etc. at typical cruise. What is a head scratcher for me in this RPM, speed, boost pressure etc. journey is my fuel flow rate in gallons per hour was an exact match to the table published by Ranger for the R25 with Cummins 150. I realize speed and RPM will vary up and down due to weight, bottom condition, etc. but our tug was way below the published data sheet for RPM vs speed. That is why I focused on prop pitch which really perked up the engine. Now I turn to finding cause for low boost and exhaust blow-by on the turbo.
Mike
 
Mike / Dan
Thanks for both of your comments. I do not have feedback from factory yet, but all of the readings they took from the instrumentation port agreed with my onboard readings. I'm sure they will have better analysis though. Will report back when I hear from them.

Mike - I am curious what you did to your prop.... Same pitch? Also, what was your speed when you got to 4050 RPM with the prop work done? I am willing to recondition my prop if it might get the performance. My prop looked brand new when I got my bottom painted last month, so did not think it needed any work....

Ed
 
Ed,

Looking forward to results. I sent you a PM a little earlier today to find out more about the service tool the Mercury technician(s) used to log data.

Regarding the prop. When I purchased the tug new the standard prop for the Cummins QSD 150 was a 17 x 15 which never allowed me to reach rated RPM (4000) at WOT. When we pulled the boat for winter storage that first year I removed the prop and had the pitch reduced to 14. The following spring first time out no change in RPM. At the end of last summer I pulled the prop and took it to another shop which actually used computer scans to check pitch. Oh boy. Not one of the three blades was at 14, only one blade came close to 14 at 14.4 and that was only on one area of that particular blade. Prop scan takes six readings on each blade and the mean average was 14.5 for all three blades. The computer analysis based on my achieved RPM vs rated showed the pitch should be at 13.2. That is what the shop adjusted the prop to and first time out this year ran 4,050. Now if I could put my finger on the low boost and turbo heat.

Mike
 
Mike,
Responded to your PM. So you know my story.
For others, the service tech recorded everything and the engine is running normally, except for hitting only 3700RPM at WOT.
The Turbo Pressures were in the normal range. Mercruiser has suggest 3 potential causes.

1. To much back pressure in the exhaust. (doubtful for my boat because just replace it all with new)
2. To much weight on the boat. - I will be offloading everything I can to lighten her up and do another trial - but can't do this until about 10 June. I will report out when I get her done.
3. Potentially need to adjust pitch on the prop - as Mike did.

The theory as to why the Turbo is getting too hot is - not enough cooling at 3700 and loading at 100%. Since the loading should max at 4050 - the extra RPM could help reduce the heat build up... Just a theory right now.

More when I know more.
Commander Ed
 
I have a 2008 Cummins 150. The turbo looks virtually new, no scorched paint or soot. WOT is 3750 with a speed of 19 MPH and boost around 16. The engine runs at 182°
When we had the marine survey, the mechanic said I should get the propeller adjusted for 4000 RPM. Will look into that, this winter.
Interesting topic, like to see where it leads.
 
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