Recently bought a 1989 Econoline RV with a 460 in it. Only 72k miles on it, should I use 15W-40 in it for higher zinc as this is a flat tappet engine I assume? Figure it would appreciate the thicker oil due to the heavy weight of the vehicle and possible towing a car/or ATV trailer behind it occasionally on trips, heat of summer and what not or would 10W-30 be fine? I have a lot of Rotella leftover from my 7.3 diesle that I sold that needs used up anyway! Just wanna make sure this is okay for the engine as I don't know much about them.