6BTA 5.9 black smoke above 1600 RPM

[Mark Kiehl]

I have a single 1998 Cummins 6BTA 5.9 M3 engine, CPL 1975 in my 1999 Nordic Tug 37 with 4251 hours on it. At speeds above 1600 rpm, I have black smoke coming out of the exhaust (more erpm, more black smoke). Power, performance, and temperatures all normal. I pulled all injectors and had them rebuilt (4 out of 6 just dumping fuel). Replaced all injector seals / washers with new, including fuel line seals. To my surprise, I still have the black smoke. Cleaned the air intake filter. Pulled the aftercooler and cleaned the air side despite the fact that it looked pretty good. Visual inspection of turbo intake looks okay (gap looks okay, and it spins). I don’t feel any play in the turbo fan. Hooked up a 10 psi pressure gauge to the aftercoler intake and measured these boost pressures: 1200 erpm: 0.9 psi, 1400 erpm: 1.9 psi, 1600 erpm: 3.1 psi, 1800 erpm: 5.3 psi (black smoke), 2000 erpm: 8.5 psi. Are those values normal? I don’t know what to do next. I suspect some sort of air intake issue, but don’t know what to try next. Please help.

Topic

[Tony Athens]

Mark,

Not sure where you are getting your info, but per the spec sheet on your  specific engine,  in a  test cell under certified/very controlled  conditions, with your engine loaded to 315 BHP at 2800 RPM, 56″Hg is the number- +/-  5%.. Understand your engine room is not controlled as to these “conditions”.

If your prop is not loading your engine to 315BHP boost will be less. 

If your engine does not make an accurate 2800 RPM (or a tad over) under load you will make less boost.   The fact that you make black smoke, generally tells me things are not as right as you may think with your aftercooler and / or your turbo  

You should let ME SEE the exhaust side of you turbo..  As to the aftercooler core-Maybe I should see that too?

Where, how and what are you measuring boost with?

 

 

 

 

 

[Mark Kiehl]

Update to CAC intake pressure question

I have been asking the same simple question since 1 September 2022:  “What is the expected air pressure to the inlet of the charge air cooler / aftercooler at rated speed? “.   I spoke to a couple of other resources, and I was told that according to Cummins QuickServe Online the pressure at rated speed should be 52 min to a max of 62 in Hg.  My measurement of 23.5 psi (47.8 in Hg) running under load at rated speed is 8.8% less than the 52 in Hg minimum value.  That value of 23.5 psi / 47.8 in Hg is exactly the same as what was measured during the pre-purchase sea trial of my boat back in 2012.  

This suggests to me that my turbocharger may have some wear, causing the output to be slightly lower than specification, but it hasn’t changed at all in  2280 hours  (4290 – 2010).  

[Mark Kiehl]

Aftercooler pressure test results

I just completed a pressure test of my aftercooler air side.  I following the Cummins instructions per ‘010-027 Charge-Air Cooler’ and pressurized the sir size of my aftercooler to 30 psi and then measured the air decay over 15 seconds.  I repeated the test 5x times with a good quality 30 psi gauge, and each time the pressure dropped a maximum of 2.0 psi.  The test requirement is that the decay is less than 7 psi over 15 seconds, so my aftercooler passed the test.  

Using soapy water, the leak is at the air crossover at either side of the heating element.  I did my best to cleanup this connection, and I had to install a temporary custom made rubber gasket to get the seal required for the test.  I just ordered replacement gaskets from sbar.com.  

So the good news is the water side of the aftercooler is not “misting saltwater into the engine combustion chamber”.  😉

[Gene Fuller]

What does the 56 in Hg / 27.5 psi mean?

Inches of mercury is just another way to state the pressure. The two numbers above are essentially the same.

For reference, one atmosphere of pressure is about 30 in Hg and about 15 psi. You can see that the numbers you quoted have the same ratio, close to 2:1.

Some gauges measure in-Hg, others measure psi, and others in more exotic scientific units.

[Mark Kiehl]

What is CAC intake pressure for 6BTA 5.9M3 ?

I have a single 1998 Cummins 6BTA 5.9 M3 engine, ESN 45777183, CPL 1975 in my 1999 Nordic Tug 37 with 4251 hours on it.  Running at a RATED SPEED of 2800 erpm, the air pressure into the charge air cooler / aftercooler was 23.5 psi, and the air pressure measured at the air intake was 23.0 psi, or a differential of 0.5 psi.  Cummins states that a differential of 3 psi or less is good (no air restriction).

 

What is the expected air pressure to the inlet of the charge air cooler / aftercooler?  I measured 23.5 psi at the aftercooler intake running at a rated speed of 2800 erpm.  The engine performance  (DS-4960, Curve No. M-90208) states “Air Manifold Pressure: 56 in Hg” or 27.5 psi. Is the air output from the turbo correct?  Or does this suggest something is wrong with the turbocharger?  What does the 56 in Hg / 27.5 psi mean?  

 

[Steve Lewis]

MK,

You do bring up a good point.  Proper engine loading.  An NT37 loaded for a long cruise is going to present a rather significant load to the engine when pushed above nominal hull speed.  CPL 1975 is the 6BTA330.  That is a 2800rpm engine.  Tony recommends being prop’d to make 105% of rated RPM so 2800 * 1.05 = 2940.  If you want to push your NT faster than hull speed for any extended amount of time then I would suggest making sure the entire system is operating properly AND you have the correct pitch to allow the engine to make 2900++ at WOT under load.    Think of it like a feedback loop.  Boat loads prop, prop loads engine, engine responds to load, needs lots of air so the turbo needs to operate properly to compress the intake air and the aftercooler needs to allow the air to flow freely through the fins to cool that hot compressed air.  That all goes into the combustion process which then creates exhaust which flows out through the turbo to cause it to spin and compress the intake air.  Any part of this system that is not working properly will negatively affect the system. Black smoke will occur.

I still recommend getting the Aftercooler and Turbo figured out before figuring proper load.  I have attached a couple things.  I wrote a Prop Tuning document. It is a guide to the whole process but you should get the cooling circuit figured out and the turbo verified first.  6BTA330 performance report.

I found the whole process of getting systems clean and proper and then dialing in engine load sort of satisfying as I know that we have a well configured system that operates well.  We enjoy stretching our cruising legs on the Great Lakes.  We have gone places and will continue to go to new places confident that our boat will work well.  It helps me enjoy the cruise more knowing that I do not have to worry much about the boat.  I just worry about the weather……

[Mark Kiehl]

Steve, Thank you very much for taking the time to provide clear and actionable recommendations.  

 

Prior to reading this, I ran the engine in neutral to 3100 rpm to confirm the throttle linkage is okay.  I reached 3100 rpm very easily, and could have gone much higher.  

 

Tony’s Tips makes mention frequently about matching a prop to the boat and the engine.  I’m wondering if the problem is simply that the boat is loaded for a six month trip, and those supplies plus all the spares and other goodies I added to the boat are causing the boat to be overloaded?   Could the problem be as simple as that, and not the exhaust, aftercooler, and turbocharger?    

 

The amount of black smoke is hard to quantify, but it isn’t something that would get the attention of most people.  Running the full displacement boat 20% above hull speed (71% of WOT) for about four hours per day for 18 days does cause it to accumulate on the back of the boat surfaces.  

 

At the present time I have actionable advice on how to evaluate the aftercooler, exhaust elbow, and the turbocharger.  Thank you.      

[Gene Fuller]

One more thing.

The Cummins folks may have been the absolute best in the world. But if the work was done in 2012 the aftercooler is way overdue for a thorough examination. The recommendation is every two to three years, not 10 or more.

[Steve Lewis]

Suggestions……. Back to Basics

MK,

Some clarity here…… Black Smoke means lack of air in the combustion system.  Either the aftercooler is messed up or the turbo is not doing its job properly.  Both need to be run down independently.  The highest probability has to do with Aftercooler(thus Tony’s 50/50 comment).  The Turbo and the exhaust setup is second………

Just because it was serviced by a Cummins Tech does not mean it was done to Tony’s specification which is the Gold Standard(better and more complete than Cummins).  Remove the entire Aftercooler unit and take it apart.  It must be taken apart and the radiator core removed.  Any thing else is incomplete.  Clean both the water tubes and the air fins as per the documented processes on this site.  Spend some time watching the Tony’s Tips video(s) about cooler maintenance.  Pressure test the core on its own(Rob Schepis posted his rig for doing this).   By doing it this way you can see if the core holds pressure over a 24hour period which will indicate leak or no leak in the core(salt water misting if there is a leak).   Then reassemble as per the documented protocol on this site.  Pressure test again both sides independently.  this will make sure that the assembly is not leaking.  If it passes at that point then you are good to move on to other things.  This is the INTAKE AIR side of the system.

Tony and Gene have told you to also focus on your exhaust setup.  Doomed to fail wet elbows will eventually back feed (salt)water into the exhaust side of the turbo and cause damage once the elbow has corroded and started to leak.  The only way to know is to remove the wet elbow and look into the turbo(well documented in Tony’s Tips).  This damage will cause the turbo to misbehave or fail totally, causing black smoke because of insufficient air in the combustion system.  Again, the only way to know for sure which side of the equation might be causing this is to take it all apart and test independently.  No half measures.

Tony wants you to follow all of his protocols to the letter and validate all parts of the system independently.  Otherwise you will be scratching your head and the forum will not be of value.

 

[Mark Kiehl]

The aftercooler service performed after I purchased the boat in 2012 was done by a Cummins certified service center.  I don’t understand you you say it was not cleaned properly.  

Recently I hooked up a pressure gauge to the aftercooler air intake, and another to the intake manifold (after the aftercooler).  I was only able to measure up to 2000 rpm because the ‘exhaust’ gauge was out of range.  At 2000 rpm, the maximum difference in pressure was 0.2 psi (the Cummins troubleshooting guide says it should be less than 3.0 psi at WOT of 2600 rpm).  The intake pressure at 2350 rpm was 20.0 psi.  At all other (lower) rpm measurements, the difference between inlet and outlet pressures was 0.0 psi.  This suggests to me no significant air restriction in the aftercooler, and the aftercooler cleaning I performed was good. 

Cummins has a an aftercooler leak detection troubleshooting process I intend to perform to address your concern about my use of a small amount of Barnacle Buster to flush the aftercooler. 

WOT test.  I tried to run the engine at wide open throttle (WOT) of 2600 rpm.  Starting at 2300 rpm, increases in throttle do not result in increase in engine speed beyond 2350 rpm.   Suggestions? 

 

[Tony Athens]

Mark, In so many words, your aftercooler has NEVER been serviced as to what matters……………

 

There is better than a 50-50 chance it is already “misting saltwater” into your engines combustion chamber..  .. Your call from here as to where you want to go as ————you need to do some research on what this is about.. I can’t offer you anything else that is not already well documented on “Tony’s Tips”…

 

PS — Your are playing with BIG FIRE here that  will lead to major $$ consequences if your do not follow my lead.      

[Gene Fuller]

Nordic Tug 37’s of that vintage came with the “doomed to failure” Cummins exhaust elbow. If it has not been upgraded it is quite likely to be related to turbo problems.

(I have a Nordic Tug 37, so I pay a lot of attention to those stories.)

Gene

[Mark Kiehl]

Regarding the aftercooler, I removed it complete from my engine.  I did not remove the core.  I hooked up a circulation pump to the air inlet and circulated Simple Green and Dawn dishwashing liquid for several hours with the entire unit in a tub.  Flushed with fresh water.  Then I ran a small amount of diluted Barnacle Buster through for an hour or so, and then flushed with fresh water for several hours.  When dry, I could blow with my mouth on the inlet end and felt absolutely no restriction.   The water side of the aftercooler looked in good condition (I have been cleaning that over the past 10 years).  The aftercooler air and water sides had been previously cleaned professionally back in 2012 (not sure if core was removed, but I suspect it was).  

I did not remove the turbo and inspect it from the exhaust side.  I had really hoped that my boost pressure measurements I provided would suggest if this was required, or not.   Are those boost pressure values in the correct range / magnitude?  Or are they completely useless in terms of turbo diagnosis.  

If you suggest to me that nothing else should be considered suspect such as the injection pump or the injectors, then I will pursue turbo removal and be prepared to replace it.  

 

[Tony Athens]

Mark,

Do this as asked:

1–Pulled the aftercooler and cleaned the air side despite the fact that it looked pretty good. 

Tell me exactly what you did step-by-step as to  cleaning the air side  On the engine, on the bench, completely disassembled with the core removed, or ??

 

2– Visual inspection of turbo intake looks okay (gap looks okay, and it spins). 

Did you look inside the exhaust side of the turbo with the elbow off?  That is side that really (only) matters with symptoms like your have. 

Until you do both of the above (#1 on the bench and in pieces) , you are chasing your tail and you will not catch it..

Tony

 

 

 

 

 

 

 

 

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