QSM 11 670HP Performance Issues (900hrs)

[Richard Lynch]

This year has troubled me… See below. 

1. Port engine has been burning more fuel (as much as 2GPH) depending on speed all season.  
2. Overall GPH has increased as the season went on…
   1. Which is typical; bottom growth, higher ambient temperatures, humidity, etc.
3. Aug 1st – Cleaned the bottom and running gear. Prop shop checked the props and said a couple blades were bent over slightly. They thought the yard may have done it by blocking the blades during install in Feb. 
   1. They corrected the Port Prop but not much of a difference noticed in Load and GPH on Port Motor. 
   2. Overall GPH came back down and could reach redline but Port Motor still burning more fuel than starboard.
4. Boat sat for a few weeks (most of August) without use.
5. Took two longer trips and slow cruised for both with blow out runs at the end of each. Couldn’t reach redline RPM (2350 rpm Redline I was maxing out around 2150-2200) for both runs. Boat felt sluggish.
6. Thought I may have growth so have tried to make a couple high speed runs but still cannot reach Redline and still burning more fuel than I should.
   1. Back to back trips now I blew the dipstick out and sprayed a small amount of oil. First time it was the Starboard motor, second time was the Port Motor.  Thought maybe the dipstick was not tightened on the first one so I doubled checked both of them but it still did it on the other motor. Just Ironic???

What the heck is going on? No relation to all of these things or do I have something larger going on… I know I need to pull the boat and check the bottom but cant believe after 3-4 weeks after complete bottom redone that I would have enough growth to make a big difference.  Could dirty Air Filters cause any of this? Both blowby filters do not have the Red Indicators popped up.  Any tips to start narrowing the issue would be appreciated.     

See picture, all temps and pressures seem to be inline. Load, Turbo PSI, and GPH are high on the Port Side 

Topic

[fixinbones]

So the boat was run again and these are my EGTs.  Again, these are QSM-11 715hp in a 4700 Tiara Sovran.    We are seeing less than 1,000deg at all rpm’s.  So I assume if I’m running under 1,000 at my cruising speeds of 2,000-2,100 my manifolds and turbos should be out of the danger zone?

[fixinbones]

Thanks for clarifying the temps.   The mechanic just got back to me regarding my boat operating temps.  Thanks The boat is running EGTs of 900 deg from 1,800-2,100.   Wot temp is 1050.

[Tony Athens]

QSM11 715 exhaust temps

As Steve pointed out, I posted the wrong temp you should use to gauge things..  Look at the attached. Things you need to know are highlited

[Steve Lewis]

I am going to refer you back to my Caveat Emptor post.  I attached the QSM11 715 performance report.  Open that up and scroll to page 3.  There is a section for Exhaust System.  There are 2 temps listed.  Turbine Out, which you should use, and the Manifold temp which Tony quoted.  Use the turbine out temp as that is where your measuring probe is located.  So it looks like WOT temp is about right.  Now you need to figure out your cruise temp.

I am going to recommend, again, that you search the forum for the answers you seek.  Search EGT as the term and refine with author Larry Backman.  He has posted extensively about his QSM, how he operates and the temps he gets.

2 users thanked author for this post.

Tony Athens, fixinbones

[fixinbones]

I’ve decreased pitch a bit and I’m still slightly overpropped but I did this on purpose as I don’t want to lose much cruising speed.  That’s why Ive installed the EGT gauges so I can watch the temps and fine tune the rpm’s where I want to run the boat.  I know i may be compromising long term engine health but that’s  a risk I’m willing to take.  I’m waiting for the mechanic to send me back the EGT plot vs rpm’s.  I did get a picture of the gauges while they were running the boat and the temp at 2530 was only 1000deg which seems low.  

[Tony Athens]

QSM 11 715–EGT Question

There is no specific answer to your question as Cummins only publishes EGT at full rated HP in test cell “perfect” conditions–Happens to be 1349F………………. With that said,  build a base on what you have to use down the road..

 

What does matter if you want any life out you your exhaust manifolds and turb0 is  your GPH (actual engine load)  at RPMs between 1800 and & 2100 RPM  Look at the attached,,

 

Do a graph like this and fill in your GPH at those RPM’s.. That will tell me the story as to what you can expect over the next few years or 500 hours of use .

 

Tony

 

 

[fixinbones]

So I’ve installed EGT gauges on the QSM-11 715hp engines of my newly purchased Tiara 4700 Sovran.  Can I get some guidance on what the maximum recommended EGTs should be when running the boat for a sustained period?  Thanks 

[fixinbones]

Thanks Steve.  Once I close on the boat I’m gonna run her and get fuel burn numbers under proper loading conditions and likely take an inch of pitch off and see where I am.  I’m also going to install EGT gauges as well and see what my temps are at varying Rpm’s

[Steve Lewis]

Caveat Emptor

What I am about to write is pure theory and outside the recommended approach that Tony and the SBMAR crew would ever make for the QSM.  To be clear, you prop any boat with any QSM to burn no more than 20gph @2100rpm. Full Stop!

That being said, the boat you are looking at buying has the QSM715 which is rated for 2500rpm.  If you read the fine print of the performance report, see attached, it reads that “reduced power must be at or below 200rpm off rated rpm”.  That means MAXIMUM SUSTAINED operation is 2300rpm.  I would NEVER recommend running these engines at that RPM in an over prop’d condition. However, if you absolutely “Have the need for speed” then join these two ideas.  Prop the engines right, 20gph @2100rpm, and THEN AND ONLY THEN run the engines between 2100 and 2250 and see how it goes.  If you are going to ask this much of the exhaust manifold then you should get EGT gauges installed and watch the exhaust temps and operate as YOU SEE FIT.  Otherwise you are running blind as it pertains to the heat going through the manifolds.  EGT gauges are pretty inexpensive options that help you dial in the compromise of getting the most speed that you can while getting the most life from your manifolds.  It is an ART not a Science.

You appear to be asking for permission to push these exhaust manifolds beyond what is known to cause issues.  You will never get that kind of guidance here.  If you want to go fast, then go fast.  Just know that it will cost you more to go fast in all sorts of ways with these engines.  If you really want to go fast in this big of a boat, there are other options out there. 

Final Thought….  The Great Leon Slikkers(Parent of the Parent of Tiara Yachts) was interviewed by boattest.com and he very eloquently said that the most expensive option on a boat is “speed”.

[fixinbones]

Surveyed and over propped

So the survey shows the boat is over propped like the Tiara spec sheet.  I’m concerned about losing much cruising speed with reducing pitch and I really would only want to go down 1” in prop pitch as opposed to  a 3” pitch reduction which is whst I think you guys would probably recommend.  I know this will lead to earlier issues with the exhaust manifolds.  What if I run the boat at 2200-2300 for cruising?  If you cruise the motors at higher rpm aren’t the motors flowing and cooling better at rpm’s above 2100 even though fuel burn might be high?  Isn’t the heat problem when u run the engines at 1900-2100?   <br /><br />Motors turned 2500rpm and 2520rpm, 38gph, 33knots, 99%load, coolant temp 170

2300-30pgh, 30knots

2200- 28pgh, 28knots, 80%load, coolant temp 165

2100-25gph, 27knots 

2000-22gph, 25 knots, coolant temp163

1900-20gph. 

[fixinbones]

Thanks for the reply.  I’m surveying the boat on the 13th and I have an engine surveyor coming and well go over the fuel burn numbers during the sea trial.  The boat has 700@hrs on the QSM 715s.  I haven’t been able to get any info on engine work history yet but I will surely compare the numbers we get at sea trial with the Tonys charts and the Tiara numbers below which shows they are overloaded from the factory.   

[Steve Lewis]

Propping the Cummins Marine QSM 11 to Prevent Exhaust Issues

I consider this article to be the definitive article on which to base your conclusions but you do have to read between the lines a bit.  The first sentence that is after the pictures states the case but then everything else at the bottom tells you that you can push things a little bit for short periods of time but in the end Tony has consistently responded to posts, like he did in this thread above, that the “Best” way to get “The Most” life out of your QSM Exhaust Manifold is to prop your boat to run 20gph (or less if you can) @ 2100.  You can run more but that will likely end in warping and leaking earlier than you want it to.

It looks like Cummins got the message and when they designed the fuel delivery in the QSM715, they did it to mimic the 535.  That is a very naive judgement on my part…….  Boat Manufacturers did these engines no favors by propping them to impress the customer as opposed to prop for long life. 

In the end, Tony says that you can not under prop these engines, only over prop them.  The more you over prop, the shorter the life will be.  It all is a matter of degree. 

1 user thanked author for this post.

Tony Athens

[fixinbones]

What confused me was these 2 graphs in 2 of Tony’s articles which shows a 21.7gph burn at 2,100rpms in the prop curve for exhaust manifold health article and another chart for the 715hp model which I’m purchasing showing a 21.5gph at 2,100rpms. 

[Steve Lewis]

Think of things in these terms.  The QSM535 fuel burn curve is what Tony has stated is the ideal.  If you prop your engine to burn at those rates then you will maximize the life of your exhaust manifolds and turbos.  They are not liquid cooled like they are on other engines.  20gph@2100 rpm is the goal as that would be the MAX sustained cruise.  When you hit that goal then you can see what the fuel burn rate is for your boat at other rpm’s.  With the QSM it is all about the amount of heat that is going through the Exhaust Manifold and Turbo.  When you get the correct loading then the fuel, air and engine cooling fluid flow at RPM all come together which results in an Exhaust Gas Temp that maximizes the life of the manifold and turbo.  That is the goal.  keep the EGT manageable.

It is very helpful to have EGT probes and gauges so that you can monitor your exhaust heat and manage accordingly.  With EGT you can see what the temp is at “the ideal” and then manage around that in different sea states, load conditions and such.  We ran the 2021 season without them and ran the 2022 season with them.  Like I stated above, small increases or decreases in rpm made changes in EGT values.  EGT also alerted me to an issue and allowed us to throttle back and drop off plane.

The consistent recommendation from Tony has and will be 20gph @ 2100rpm for the “Dry QSM” of any rating.  The base engine is very stout.  It is the bolted on accessories that are the weak links.

[fixinbones]

I’m a little confused regarding the proper fuel burn to avoid exhaust gas issues.  This thread mentions 20GPH at 2,100 but I’ve read in one of Tony’s articles about shooting for less than 20GPH between 1900-2000.  I’ve also read that if you want to burn 22GPH it needs to be at 2,100rpms  So what should I shoot for at 2,000 and 2,100 on a QSM 715hp. I was thinking that <20GPH AT 2,000 and up to 22GPH at 2,100?   Comments appreciated.  

[Tony Athens]

Read the  answer from Steve Lewis….

 

The goal is 20 GPH at 2100 rpm not 1950..

 

If you do not want to listen to 30+ yrs of experience with this engine, then neither myself or other with experience can help you…

 

Tony

[Steve Lewis]

Richard,

The goal is 20 GPH at 2100 rpm not 1950.  That 150 rpm difference causes a lot of heat in the exhaust and excessive exhaust heat is the mortal enemy of your engine and mine.  There are 3 articles in the Tony’s  Tips section dedicated to the QSM and exhaust health.  They all end up recommending 20GPH@ 2100.

I installed Exhaust Gas Temp probes and gauges this year and have been using them and messing around with different RPM running.  I can see EGT decrease when I advance the throttles from 2220 – 2300.  I can also see an increase in EGT when we back off to 2100.  What looks like small moves on the RPM dial translates to some pretty big temp swings in the EGT.  The only way to see that is an EGT gauge.

I took 2 inches total out of our props and I am about 1 gallon per hour per engine over the mark at 2300 depending on load.  Our engines(6CTA480CE) have cooled manifolds and Turbos so the issue I need to remedy is the Exhaust Valve Seats.  New cylinder heads this off season.  We did all of the proper mods first to dial in engine load before having the heads replaced.  Order of operations is important for remediating these types of issues.

Your vessel speed is ~24.6mph @1950.  To save the long term life of your engines you will need to pitch down even more than you have already which may translate into running a little slower from a vessel speed perspective while the engine is turning a slightly higher RPM.  With the QSM it is 20GPH at 2100rpm and let the speed chips fall where they may.  Our vessel speed is ~22.5 on a cruising load and will increase to 23.5 – 24 as we burn through a load of fuel.  For me, Peace of mind is worth sacrificing a couple of miles per hour.  Your call and wallet.

Search the forum for author Larry Backman.  You can read his experience and EGT values for his QSM.  It is instructive and can give you extra guidance.

[Richard Lynch]

Yes but…we reduced pitch to 20GPH@1950 see attached

We replaced the manifolds in 2020. We also took 2″ of pitch out of the props to get to the 20gph range at 1950 or so… 

The issues I described in the first post are as of this year. Maybe a result of what your saying but was thinking something else was going on since I was at or very close to that sweet spot…        

[Tony Athens]

QSM 11 ———–Over Loaded

Richard,

You are not going to like what you are going to hear from me………………..Your engine are GROSSLY OVERLOAED and you  have fallen into the  “making rated RPM” or “close enougt” and think you are OK………… 

# 1——You do not cruise at WOT so you SHOULD not use that and any type of load indication for this engine–It does not apply

#2–The prop curve on this QSM rating at your cruise RPM on about 1990 RPM is about at 20 GPH.  You are at 23 GPH–That is Black & White

 

#3 –For well over 10 years my propping  recommendations on a DRY a QSM11 is well documented

 

Until you prop down about 3+” of pitch, you WILL NOT fix any of your current issues.. Your are literally “strangling your engines” to an early death and from what  I see , you are already there as to your manifolds and turbo–Plus,  your aftercoolers are most likely clogged with exhaust soot by now…

Listen, or be in denial—You are not alone with your symptoms and what you need to do—————————Your call.

Tony

 

 

[Richard Lynch]

Additional info…

I have a small amount (more on the Port side) of soot showing up behind the exhaust outlets on the hull this year. Do not recall this over the previous few years.  Oil/Filters changed yearly. Exhaust Manifolds replaced 2020, Aftercoolers removed, cleaned, tested Sept 2019. Elbows & Risers replaced 2021.  Valves adjusted in Sept 2019. Installed SBMAR Air Filters in 2020.   Purchased the boat in Aug 2019 with 550 hours.     

[Author]

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