I too am of Jerry's understanding. But as opposed to 15-40. I generally use 20-50. But only on "high milers". Reason being;
the higher viscosity helps "fill" the larger "gaps", and helps prime the oil pump faster in the morning, when the rig is first
started. Potential downside; it's harder on seals, and gaskets (higher pressure).
That said. It's always been my understanding, and belief that for a new(er) motor. Single weight oil is a better choice.
Multi-weight oil is achieved by adding polymers (plastic molecules (balls)) to the oil. So it's actually more stable, and
durable than multi-weight oils.
Lastly, and along the lines of "washing" the crankcase; I usually dump a half a quart of tranny fluid in the crankcase
about 50 miles before an oil change. Because tranny fluid is such a high detergent oil. It helps thin, and loosen
any gunk that might be forming anywhere. Not good for an old "loose" engine. That "gunk" helps, more than hurts.
--Chris
