All, Well, I've done it now. I brought home a new class A. Mine is on the FORD F53 chassis. The oil fill cap & owners manual state it is to use 5W20 motor oil ? WOW! That sure is thin....
Maybe this will clarify. I asked the same question on the V10 to my mechanic and race car friend and his explanation makes a lot of sense. The oil type is determined based on the manufacturing tolerances in each engine. As tolerances get smaller, the oil needs a different viscosity. Using any weight other than recommended is a gamble.