Hate to ask a GM question...

[shady]

here you go.

https://bangshift.com/general-news/tech-stories/is-the-factory-wrong-about-which-oil-you-should-run-in-your-late-model-car-stop-following-oem-oil-advice-the-recent-gm-recall-proves-why/

[Barry_R]

Rod bearing failures are always a treat to get to the bottom of because the failure mode is so rapid and destructive, rarely is there any good evidence left behind to help determine what the problem was or the root cause.  Some of the failure modes that I have seen analyzing warranty engines at work are due to the following.

1.  Contaminated / Dirty / Old / Overheated Oil.  Oil with coolant, fuel, dirt, etc can take out rod bearings quite quickly.  Navistar, Ford (6.OH-No!), and CAT engines from the 2000's and 20-teens that used EGR extensively to meet emissions are particularly prone to this.  EGR cooler develops an internal coolant leak, and all the sudden your engine is trying to lubricate with the green stuff.  I have also seen a bunch of rod bearing failures in air cooled engines due to oil overheating.  When I was at a small engine manufacturer, the life span of the rod bearing was measured in minutes once the oil hit 350 deg. F.

2.  Machining Quality.  Everything from surface finish, journal roundness, corner radius all can affect the lifespan of the rod bearing, and it doesn't take much of a deviation or miss to shorten the life span from 100,000's of miles to 100's of miles.

3.  Engine (casting) Contamination - See recent Toyota Tundra recall

4.  Crankshaft design / flex.  If the crank flexes more than intended or designed, bearing failure can result.  Typically this is more of a main bearing related problem, but it can lead to rod bearing damage as well.  PACCAR 13L engines are known to experience more crank flex than intended and this will lead to failed bearings.

5.  Rod Bolt Quality.  About 3 years ago, we started seeing a dramatic rise in rod bearing failures on Navistar I-Series reman engines.  Turned out, the rod bolt manufacturer (Navistar chosen and vetted supplier) had changed their process and the bolts were softer and did not have the designed tensile strength.  Bolts would stretch and lose clamp load on the cap, and the bearing would spin.  We discovered the problem by doing an extensive statistical study on our DC tool data (torque and angle) from assembly.  The failure rate was only 3 to 5% of engines, so it was difficult to catch, but there was a statistical change in the data.  The bolts were close to being correct (a measured sample would often meet the engineering print and specs), and they would even torque, yield, and stretch properly during assembly, but would fail within 10,000 miles.  We went down a number of rabbit holes before we figured out the root cause on this one.  Navistar ended up recalling all the rod bolts at their dealers and assembly facilities.

6.  Bearing Material or Quality.  Doesn't take much of a change at the supplier to cause problems in the engine.

This would be a good "guess" - the bearing is the "victim" of something else in the system.  Could be damn near anything.  Given the level of electronic management in a new engine package, it could even be something in the software that controls timing and fuel.  A bearing (or rod etc.) design that just meets or barely exceeds design needs won't have enough "headroom" to handle any unexpected loads.

[Katz427]

According to the  Chev dealer local, the problem is crankshaft surface finish. I am surmising that going to a heavier oil, just delays the inevitable failure.

[FrozenMerc]

This would be a good "guess" - the bearing is the "victim" of something else in the system.  Could be damn near anything.  Given the level of electronic management in a new engine package, it could even be something in the software that controls timing and fuel.  A bearing (or rod etc.) design that just meets or barely exceeds design needs won't have enough "headroom" to handle any unexpected loads.

Your right, the bearing is normally the weak link that results in engine failure, rarely the actual problem or root cause.  I have seen something similar on 3.9 Cummins 4BT Industrial motors.  Ran fine and forever at the factory rated 85 Hp, but as soon as farmers started fiddling with the fuel pumps and attempting to squeeze a bit more power out of them, the rod bearings would quickly fail.  Granted these were cheap aftermarket bearings, not Cummins OE, but the difference in lifespan between a stock 85 hp motor and one that had been turned up was startling. 

According to the  Chev dealer local, the problem is crankshaft surface finish. I am surmising that going to a heavier oil, just delays the inevitable failure.

If the root cause is incorrect surface finish, changing oil viscosity will do very little to help, and it might actually make it worse as the thicker oil just causes the Oil Pressure Relief Valve to open further and you see a larger pressure drop from one end of the crank to the other.  In other words, the bearings furthest from the pump may be getting starved, especially at startup and low operating temps when the oil is at it's thickest.