Always learning. Can someone explain any of this? My oil analsis '89 Cummins with 505400 showing on the odometer (not sure if orginal engine). Using Amsoil S3000 syn hd,slowly changing to 15-40 diesel & marine syn. Running Frantz & Amsoil filters,sampled at 5000 miles use. As follows: iron-18,chromium-2,lead-4,copper-3,tin-0,alum-2,nickel-0,silver-0,silicon-5,boron-6,sodium-3,mag-83,calcium-3545,barium-0,phosp-1358,zinc-1691,molybdenum-3,titan-0,vanadium-0,potassium-0,fuel<1,vis@100c-12. 46,water-0,soot-0. 2,coolant n/a If anything my typing skills are improving. At 5000 miles changed the toilet roll. The analysis was from Staveley Services,tried calling them didn't get any advice. Have no idea how long to go on the oil? Do the same thing at the next 5000? Will this oil hold up to 20000 miles? The old girl runs great, hate to blow a good thing. Many thanks in advance. Scott