X2 !, the multi-grade diesel oils are a good choice, especially for Florida, IMO. They are usually inexpensive ; I recently bought a five quart jug of Rotella for under $12.00 for one of my tractors. The 15w40 will probably serve to avoid the pressure relief when cold, and still maintain current hot idle pressures. For my personal use, I prefer to avoid stressing components needlessly. I subscribe to the popular rule of 10 psi per thousand rpm, and don't care to find out which is stronger, the relief devices, or the old oil pump drive. If the factory recommended oil viscosity will hold that minimum pressure in all situations, I see no reason to add extra resistance to the system and take a chance on either relief system failing to reseat.
Years ago, I religiously ran 20w50 oil; now I'm convinced that is seldom needed in a solid street engine.
Years of turbo experience has proven to me there is a considerable difference in "hot" viscosity of oils with the same stated grade range; the popular diesel oils excel in retaining hot viscosity, even when compared to some expensive "turbo" oils.
Paul
