Took delivery of a Torch Red 2003 Mach 1 5 speed back on July 25. 4.6 liter DOHC 305 hp v-8. I have been using 10w-30 Mobil 1 in both my Ford Excursion and F-250 SD Crew Cab, both with V-10 OHC engines. I wonder about this oil in the DOHC engine, or should I go with 5w-30. Can't bear the thought of using 5w-20 oil. I changed the factory fill out at 400 miles and put in Mobil 1 5w-30 with a new filter. Any thoughts? thanks...Ken.