Rewarding. Frustrating. Worthwhile. Or somewhere in between…
By Steve Scott
Failure analysis of heavy-duty diesel and natural gas engines can be one of the most rewarding—or most maddening—parts of the job. Some failures practically diagnose themselves, while others seem determined to stay unsolved. And then there are those moments when, no matter how much experience you bring to the table, you just can’t find the root cause. Frustration sets in.
The reality is, like one of those old puzzle games stashed in the back of the closet, all the pieces may not be there. When something fails in a loaded engine, evidence can be lost or destroyed in seconds. Parts melt, surfaces grind, and evidence disappears. It’s not always a fair fight.
Read this article with all images in the digital issue of Engine Professional magazine https://engineprofessional.com/2025EPQ3/#p=90
Engines don’t fail without reason but discovering that reason is often like reverse-engineering chaos. Whether you’re a seasoned rebuilder, a service manager, or a shop owner, asking the right questions early can make the difference between solving the mystery—or making it worse. This guide isn’t a magic key, but it is a starting point—a structured way to think through what went wrong and why. Consider it a mental checklist for navigating the some of the gray areas between what’s obvious and what’s been obliterated.
Questions and causes for oil consumption; piston seizure; and cylinder liner, head gasket, valvetrain and bearing failures will be addressed in this article. The initial inspection and fact finding are critical in failure analysis.
Oil Consumption
What to ask:
• What does the ECM data show? Idle time, load, event or abuse codes?
• What break-in procedure was used?
• When did it start?
• How much oil is it using?
• Have you checked external leaks; turbocharger(s); air compressor; type, brand and condition of the oil?
• What have you changed? Recent repairs? Other components replaced or failed?
Common Causes:
• Break-in: Proper break-in is required to seat the piston rings. For rings to seat sufficiently, load and temperatures must be applied and maintained throughout the break-in process.
• Leaks: Can be external or internal into other components.
• Idling: The top cause of poor break-in; causes liners to glaze and rings cannot seat properly; creates carbon build-up.
• Debris: Abrasives damage ring and valve sealing faces; Damages the liner crosshatch.
• Worn rings, guides, turbo, and air compressor: Worn components lose their ability to maintain oil control.
• Intake or exhaust restrictions: Increase or decrease block pressure intake or exhaust restrictions.
• Failing turbocharger(s)
• Failing air compressor
Piston Seizure
What to ask:
• ECM data is extremely important on this type of failure.
• Miles or KM on parts?
• Which cylinder(s) failed?
• Condition of other cylinders?
• Break-in and pre-lube process?
• Coked (burnt oil deposits under the piston crown)?
• Condition and part number of the cooler tubes?
• Condition of the connecting rod bushings (small end) and bearings (big end)?
• Parent bore blocks – was a stress plate used when the cylinders were honed?
Common Causes:
• The primary cause is cylinder overheating
• Altered performance specs (improper emissions deletes)
• Piston cooling tubes (plugged, bent, incorrect)
• Rolled liner seal(s)
• Failing injector
• Low coolant levels
• Intake or exhaust restriction
Cylinder Liner Failure
What to ask:
• ECM data is extremely important on this type of failure.
• Scored, seized or pitted?
• Localized or full circumference?
• Cracked?
• Vertical or horizontal?
• Condition of the liner seal(s)?
• Condition of the remaining cylinder liners?
• Condition of the cylinder block receiver bores?
Common Causes:
• Cylinder overheating
• Not supported properly by the cylinder block
• Cavitation: Poor or weak coolant; liner movement; air bubbles in the cooling system
• Electrolysis: Electric current in the cooling system
• Incorrect liner protrusion
• Impact damage
• Abrasive damage
• Overheating
• Poor head bolts
• Over torque
Cylinder Head Gasket Failure
What to ask:
• ECM data is extremely important on this type of failure.
• Liner protrusion?
• Liner fitment to cylinder block?
• Spacer plate specifications?
• Head bolt conditions?
• Torque value and process?
Common Causes:
• Altered performance specs (improper deletes)
• Incorrect protrusion
• Worn cylinder block receiver bores
• Block, head, and spacer plate surface finish
• Overheating
• Poor head bolts
• Under or over torque
Valvetrain Failures
What to ask:
• ECM data is extremely important on this type of failure.
• Valves: Lash (adjustment); stem or face wear; fractured, bent or burnt?
• Guides: Side loading wear; seizure?
• Valve Inserts (Seats): Cupped, cracked?
• Springs: Broken; tension; coil bind?
Common Causes:
• Concentricity between these components is critical
• Foreign debris
• Worn rocker components
• Valve lash (adjustment)
• Overheating
• Abrasive wear
• Altered performance specs (improper deletes)
• Corrosion
• Overspeed
• Coil bind
Bearing or Bushing Failures
What to ask:
• Type of bearing (main, connecting rod, rod bushing, cam bearings, etc.)?
• ECM data is extremely important on this type of failure?
• Condition of related bearings?
• Maintenance records?
• How related components were qualified for reuse
• Bore and journal dimensions
• Surface conditions between the casting and cap?
Studies Show:
• Over 45% are caused by dirt or debris
• Nearly 13% are caused by improper installation
• Over 12% by misalignment
• Over 11% by insufficient lubrication
• 8% due to overloading
• Nearly 4% from corrosion
• Over 3% due to journal profile or finish
• The rest due to other issues, or a combination of these causes.
No checklist can cover every possible failure, and some investigations come up empty. While a defective part may be the culprit, assuming so from the start risks missing the real cause. The goal of failure analysis isn’t to assign blame—it’s to understand what happened, why it happened, and how to prevent it from happening again. That takes objectivity, curiosity, and a commitment to following the evidence wherever it leads. Just like that half-finished puzzle in the closet, the picture may never be fully complete—but with methodical observation, thoughtful questions, and experience on your side, you’ll likely to piece together the story.
For further reading and hands-on insights, check out the archived failure analysis articles from Engine Professional magazine—they may be a valuable companion in your tech toolbox. A list of failure-related articles can be found here: engineprofessional.com/failure-analysis-articles.
Read this article with all images in the digital issue of Engine Professional magazine https://engineprofessional.com/2025EPQ3/#p=90