RE: 10w-30
*I realize this is an old thread but worthy of making comment.*
First off, the 'W' in oil identification does not mean nor stand for *winter*. The 'W' refers to 'weight' or viscosity of the oil (ie 15w40 is the API or american petroluem institute rating).
If your operating in severe cold weather, a 5w30 oil works fine without using additives. Lower viscosity rating means easier flow at cold start.
15W40 is common among all fleets, commercial rental or otherwise and considered a practical choice too for year round use. Even in Ford's 7.3 diesel's.
Using additives is Ok in some opinions and not in others. So it is a 50/50 split. (Sorry gang, your getting a diesel mechainc opinion here)
With small application diesels ( 6.2,6.5,6.9,7.3's & DuraMax) faithfully change that oil EVERY 3000 miles. Ryder,Rollins & Penske do it period. If the big dawgs do it, doesnt it make sense for you?
Mid range & heavy duty diesel are different due to oil pan & filter capacities (7-8 qts vs 20-25 qts)
You may torture me here, lol