I have been researching Rotella T5 10W-30 API CJ4 rated synthetic blend oil, and like all CJ4 oils, the ZDDP level is lower than when the 6.2L diesel was designed, and what the oils it was spec’d to use had. So as I have done since I started using this engine two years ago, I added one pint of STP for each gallon of oil. I have always used Rotella T3 15W-40 with STP. My oil pressure cold was 40 PSI idle, 55 PSI at 2,000 RPM, and hot oil pressure was 20 PSI at idle and 40 PSI at 2,000 RPM.

After liking what I read about this oil, and the positive feedback from Cummins and Powerstroke owners, as well as from a few Duramax owners I am friends with, I decided to give it a try. Like always, I mixed in my STP, one for each gallon jug, and filled the engine with the 10W-30 sauce. The oil has increased my cold oil pressure to 45 PSI at idle and 65 PSI at 2,000 RPM, and my hot pressures are now 30 PSI idle and 45 PSI at 2,000 RPM. I always thought that a thicker oil equaled higher oil pressures, but it is obvious that this is not always the case. I am curious how it will perform over the next 4,000 miles.

1993 Chevy Suburban
6.2L Diesel Engine Conversion