rt138State Route 138 (SR 138) is an east–west state hhway in the U.S. state of California that generally follows the northern foothills of the San Gabriel Mountains and the western MojaveDATA & SPECIFICATIONS RT-138 Issue 1, Page 11 13 Cylinder oils of excessively hh BN for the fuel sulphur can lead to excessive piston crown deposit accumulation. Piston crown deposits need to be carefully monitored