Cylinder 6 Failed

[Envirotec]

Hi All,

Our 2018 Freightliner Cascadia with a Cummins X15, which has approximately 17,500–18,000 engine hours, was found to have oil leaking into the exhaust manifold on all six cylinders, with cylinder #6 being the worst. What initially led us to investigate was the truck repeatedly setting 1922 codes and eventually derating or shutting down due to DPF-related issues.

We performed an EGR tune-up, cleaned and replaced DPFs and DOCs, but the problem persisted. At that point, I concluded the source of the issue had to be upstream of the aftertreatment system. After tearing down the engine, we found that cylinders 1–5 had liners and rings that appeared to be in good condition. However, cylinder #6 had a broken ring, and the liner was completely smooth with no visible crosshatch pattern remaining.

In addition, two other tractors in our fleet have recently failed the Cummins Insite cylinder performance/compression test, and in both cases only cylinder #6 failed. These are three separate X15-powered trucks (model years 2018, 2020, and 2020), all exhibiting issues related to cylinder #6.

I am beginning to believe that many of the recurring 1922 and DPF-related issues on these trucks may be the result of engine wear rather than the more common causes associated with the EGR or aftertreatment systems. My question is: why does cylinder #6 appear to be failing on all three X15 engines? Is there a known reason that cylinder #6 experiences accelerated wear or lower compression on these engines? Is this condition preventable, or is an in-frame overhaul ultimately the only solution once these symptoms begin to appear?

Thank you in advance!

[Rawze]

(my thoughts)...

lugging them to death at below 1500 rpm their whole life comes to mind.


Also, if the bore was smooth on them, they were likely seeping coolant into the cylinder due to injector cup or other seepage.

and if you got 800k+ (18,000 hrs) miles out of them, that is not out of the ballpark. Depends on what What is the power/torque rating on them?.

and was an EGR tune-up done every year?... or only when you had issues?. - It should have been done once a year.

[Envirotec]

The truck has approximately 550,000 miles and over 17,500 engine hours, all accumulated through local and regional driving. It is equipped with a Cummins X15 Efficiency Series engine rated at 450 horsepower and 1,650 lb-ft of torque, as I understand it. Routine tune-ups were not performed until I began working with the company. However, when the EGR service was completed, the plumbing and ports were not as heavily sooted and carbonized as expected.

During inspection, cylinder 6 was the only liner found to be smooth with a broken ring, while the remaining cylinders appeared to be in good condition. I was told that cylinder 6 may experience higher heat concentration compared to the others, which could be a contributing factor to the observed wear??

[Rawze]

more thoughts...

Cyl 5 and 6 usually endure the most torture in an ISX in general...

== Cyl 6 has the most mechanical lag. The cylinder head valve operation, mechanically is the furthest away from the piston operation. This is also why other brands of engines re-designs have gone to a rear valve train, which does indeed help with this.

== Cyl 6 suffers the most heat buildup under high loads.

== Cyl 6 has been known to have cavitation in the 1400-1450 rpm range due to intake design, causing a higher amount of in-rush air due to angle of the intake manifold .. although the intake manifold has baffles to help balance it out. - Some people use after-garbage intake manifolds without proper baffles in them, which is a bad thing because of just this.

[Envirotec]

Do you think the DPFs constantly plugging (1922) was caused by the cylinder #6 issue, along with some coolant leakage and worn valve guides/seals, all resulting from normal wear and tear associated with 17,500 engine hours? Is any of this preventable or is it overdue for a rebuild?