The 3.0l Duramax is a different animal, it should be designed for Low RPM/High Torque operation. Torque pec for the LM2 is 460 ft/lbs Torque at 1500 RPM, the LZ0 is 495 fl/lbs Torque at 2750 RPM.
The L87 6.2l is designed as a higher RPM motor. Torque Spec is 460 ft/lbs @ 4100 RPM. However the L87 6.2l rarely runs above 2000 RPM in my experience. On the surface this looks like a non issue, however, with the 10 speed transmission and the Torque the 6.2l puts out at lower RPM, the engine is often operating at 90+ plus actual torque at RPM ranges between 1200-1700 in these larger trucks based on how they are configured. This puts an extreme load on the engine components, oil film and even sets up a perfect storm for Low Speed Pre Ignition (LSPI). I am working on gathering some data on how the 6.2l behaves on the highway pulling gradual grades. What I am seeing is a bit disturbing with engine Torque loads over 50% for a good portion of the drives and peaks up to 95% at 1600 RPM. This clearly shows the 6.2l is behaving more like a Diesel than a typical gas engine in these trucks. Base on preliminary info on the 5.3l engines, they do not generate near the amount of low end Torque and the trucks are confirgured to downshift and the engines tend to operate at higher RPM's when pulling inclines and grades.
The L87 would be much happier operating at 2500+ most of the time, but due to fuel ecomony requirements, this is not in the cards for this engine in these 6000 bricks. I have not seen the levels of failures in the smaller vehicles using the same basic 6.2l configuration.
Again, the basic gasoline V8 design has typicaly been for higher RPM operation than Diesels. Diesels tend to have design considerations to support very Low RPM/High Torque operation, probably larger/wider connection rods, larger bearing journals, larger and wider bearings and so forth. Diesels also are not impacted by LSPI as they are not spark ignition engines, so this alone could be a big difference in the heavier vehicles.
Based on some of my conversations with oil analysis staff, they are telling me 0W20 is not an ideal oil for the Duramax. I assume this is based on lab testing results, the Duramax engines do not appear to be failing catasphopically like the 6.2l, they may be showing elevated signs of bearing wear that may only show up in much higher mileage situations? I also assume fuel dilution of the engine oil is also a consideration for the Duramax as well which would reduce the oil viscosity at the miles accumulate on the engine oil. I did not get into a detailed conversation about the Duramax as I am mainly focused on the 6.2l engines. Just passing on what I was told.
