Background: 2003 Dodge 3500 - Cummins 24V (Commonrail) - 6 spd - 4 door - 4x4 - Dually (Modifications: S&B Intake System, 100HP Tune, 4" Exhaust) Dodge only recommends the use of an approved 15w40 in this engine, period. Based upon Dnewton's experience (and others) we decided to give Rotella T 10w30 a try. This OCI was simply a test to see if the 5.9 Commonrail Cummins could survive on a 10w30. It should be noted that this OCI began with the addition of a 100 HP tune. Probably 750 miles was towing ~12,000 pounds. On the cold mornings through the winter it was allowed to idle 10-20 minutes before driving. This OCI saw the addition of a 100HP tune. We are very interested to see if the extra fuel/timing/boost has increased wear or if fuel shows up in the oil. Previous Rotella 15w40 UOA: http://www.bobistheoilguy.com/forums/ubb...316#Post1984316 Oil - Shell Rotella Triple Protection 10w30 Oil filter - Mopar Air Filter - S&B Intake System Miles on unit @ test - 115,000 Miles on oil - 6,500 Make up oil - 0 Blackstone Comments: Consider your test passed. This oil held up well, and given the still low wear, we think it did a fine job of keeping engine parts well lubricated. When you change your oil, a fair amount (10-20%) can remain in the engine, and the fact that you were using 15W/40 last time is probably why the viscosity was just a pinch high here. The true test will come if you run this oil again (with less residual 15W/40 in the block) and you still get good wear. The TBN held up nicely, and read at 5.7 at the time of sampling. No fuel found. Try for 8,000 miles. Looks good! Actual numbers on left & Universal averages on right: Aluminum 2/3 Chromium 1/3 Iron 17/33 Copper 2/3 Lead 4/2 Tin 0/1 Molybdenum 1/41 Nickel 0/0 Manganese 0/1 Silver 1/0 Titanium 0/0 Potassium 3/2 Boron 31/56 Silicon 3/6 Sodium 3/5 Calcium 2298/2698 Magnesium 10/336 Phosphorus 1020/1094 Zinc 1191/1290 Barium 0/0 SUS Viscosity @ 210*F - 69.5/59-65 cST Viscosity @ 100*C - 12.81/9.9-11.9 Flashpoint in *F - 430/>410 Fuel % - <0.5/<2.0 Antifreeze % - 0.0/0.0 Water - 0.0/0.0 Insolubles % - 0.2/0.6 TBN - 5.7 Conclusion: Dnewton is correct in that you do not need high dollar synthetics or "thick" oil to protect a diesel that gets worked. That is not to say that high dollar synthetics or "thick" oils do not have their place, just that the average user (average being use, not abuse the truck) does not need them. Now if you will excuse me, I need to find some discounts on Rotella T 10w30.