[Mark Kiehl]

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]

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”.  😉

[Mark Kiehl]

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?  

 

[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.      

[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? 

 

[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.  

 

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