I'm currently running 5W40 MOBIL because it was on sale last year at AZ for a price I couldn't refuse. I prefer ROTELLA T6 5W40 though. I don't get the infamous typewriter click with the ROTELLA 5W40, but I dod with every other oil I have tried. Also I held better hot oil pressure with the ROTELLA than I do MOBIL(not much, I hold about 30 with the MOBIL, but ROTELLA rarely dropped below 35 even hot towing).