Locked Turbo on low time QSB 6.7

[bdunigan]

I bought a Sabre 42 in March 18 that had its port turbo replaced the prior June 17. This boat is a 2013 with Cummins QSB 6.7 380hp units tied to Zeus 3000 pods. 323 hours now. 272 hours at time of purchase. 237 hours at time of turbo replacement. I just received a copy of the repair invoice which reads as follows:

…Port engine has lack of power. Noted excessive oil from the after cooler condensation valve, removed the Air Sep element and inspected the turbocharger – locked up…

The technician proceeded to replace the failed unit with a factory reman turbo. I have checked the part numbers with Cummins and the correct unit was used (though I would have preferred a new unit).

My first question is ‘what could cause this turbo to fail so early in its service life’? Where did the oil in the AC condensation valve come from? Does the oil and the turbo failure indicate any other causal issues? Service records are acceptable on this boat with annual oil services done as expected.

At this time, the port engine does not quite develop full power. (Starboard engine does.) Cummins calls for 3000rpm WOT and Sabre test numbers call for 3050rpm WOT. The port engine achieves 2920rpm at WOT. Interestingly, at 2300 rpm, the port engine turbo boost is 14.5 pounds while the starboard engine turbo boost is 12.9 pounds. At WOT, the port engine turbo boost is 24.5 pounds while the starboard engine boost is 27.5 pounds. Is this significant? Does this indicate further issues?

Props are stock units from Sabre…Z15/Z14 dual Zeus pods props.

Topic

[bdunigan]

Additional Pics

Here are further pics including the exhaust running to the pod. I will have performance data on Friday night.

[bdunigan]

PICS

Here are some pics. I made every effort to depict the entire engine as installed but it is difficult given the limited space. I have included detailed pics of the turbo/exhaust setup. Please let me know if these are sufficient or if better shots are needed and what kind. Many thanks.

[Philip]

The pictures of the engine are needed as installed. We need to see your engine as it sits in the boat from far back in clear focus so we can see what Sabre did. We are familiar with the base engine as delivered from Cummins.

As for the upgrade I’m not sure it’s that simple nor cost effective. Others will have to advise on an ecm/hp upgrade and if it would solve an overload issue. I suspect it’s an ecm, possibly injectors, and maybe even an injection pump which would be way more expensive than a prop adjustment. We can’t even tell if you need a prop adjustment until we see rpm and fuel burn number from your boat every 200 rpm from idle to max…

So we are waiting for 2 items:
1. Pictures
2. Fuel burn vs rpm numbers

Phil

[bdunigan]

There may be another solution. These QSB 6.7 380hp units can be boosted to 425hp with a software upgrade. On Sabre units with the 425hp engines, Sabre uses the Z18/Z17 props. Maybe I could have Cummins execute the software upgrade but leave the original props in place. Just a thought…

[Philip]

It’s not at all uncommon for manufacturers even quality ones to have no clue as to proper exhaust design. Even Cummins themselves builds an elbow that is poor design.

As to th oil, it most likely is coming from overloaded engines (need to reduce prop pitch). You need to post rpm and fuel burn at 200 rpm intervals for us to comment positively but I’ll bet your fuel burns are over the recommended for the engine. This again is a common issue for the factories as they prop the boat for marketing performance empty and along comes an owner who operates the boat real world (ie heavier) and the engines are overloaded.

Phil

[bdunigan]

Engine pics

Phil, while I won’t have pics until tomorrow, Seaboard has an excellent series of shots of the QSB 6.7 included in this link:

Cummins QSB 6.7 Specifications

These shots are my engine exactly (horizontal after cooler).

While these don’t fulfill your request for pics, do they tell you anything about inherent design flaws with the 6.7 turbo?

Pics to follow.

[bdunigan]

Many thanks

Phil, thank you for your quick and informative reply. I will post shots in the next day or so. I wasn’t expecting to hear the exhaust might be the culprit. One would think Sabre, after building dozens of these units, would have nailed the exhaust design. That said, I will investigate.

Is the “oil in the after cooler drain valve” comment by the technician consistent with possible exhaust issues as the cause? In other words, if the turbo has water intrusion and locks as a result, how does oil get to the after cooler drain valve? I assume the oil is coming from the failed turbo. Correct?

[Philip]

Welcome to the forum

Your not the first person to have these issues. What you need to understand is that the builder design and specs are most likely the issue. Builders design and spec a boat for marketing and performance not reliability and long term life.

First post up some pictures clear, in focus, wide angle, from all sides of your engines.

Now spend some time reading this article several times and then read it again in your engine room to understand your exhaust design.

Everything you Need to Know About Marine Exhaust Systems

Then get your exhaust off and post some pictures of the exhaust side of your turbo. Then read this article several times and compare the pictures.

What a Marine Diesel Turbo should look like when Inspected

Finally you probably would benefit from reducing the pitch of your props. Here is a final read for you.

Is my Boat Over-Propped?

My guess until we see pictures (and a VERY common issue among builders) is your exhaust design is most likely allowing water into your turbo which is why the turbo is failing in such short order and will continue to do so until the exhaust is redesigned.

Post up those pictures….

Phil

[Author]

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