after 50000 or 60000 miles of wear the clearences are no longer the same ,they are larger and a slightly heavyer weight oil will in fact preform the task of keeping a nice oil wedge between the bearing and the crank very well. also with wear the oil pump will no longer deliver the same presure as it did when new . all I'm saying is a slightly heavyer weight oil will work well .I have had over 20 6.0 engins apart for rebuilds (they go about 160000 miles on trucks that have been maintained) and a lot less if you tow heavy up hills in the Arizona heat . we have put 15/40 Dello in a 5.3 in an Avalanche with81000 on it and it now has 120000 and it is still running great and he pulls a 24 ft Cobalt boat to lake powell 30 times a year and the boat and trailer is 8700 lbs ,it does not use oil between changes.now if the temp drops below 32 degres it's a diff story . what I have found is the best in an ls1 type engine in Arizona heat is red line oil ,Mobil 1 in 10/30 is almost as good and cheaper and you can get it at Wmart or Costco for under $30.00.
