My brother has purchased a Chris Craft Sportfisherman with twin 454 Big Blocks. The engines are originals, although are 1979, with approximately 1000 hours (documented). His question is whether to use Mobil 1 10/30, or Mobil 1 20/50. The boat will be run in the waters of Cape Cod, which vary from warm bays to cold open ocean. All advice will be appreciated.
