Thanks for the replies. I have to say I am surprised by the lopsided results. I did a search on this subject before posting this poll, but thought it was worthwhile to revisit the issue.
To me, it seems unusual that a thinner oil (synthetic) could protect as effectively as a thicker one. I have noticed over the years that the automobile industry has consistently moved to lighter multi-weight oils. I remember when 10W-40 was the standard. Now, that has gone the way of the dinosaur. Apparently fluid technology and engine designs have progressed to the point where my 'old-school' theories no longer apply. Looks like I will keep synthetic in all three holes as most of you suggest. I will have to check the availability of brands like Redline and Amsoil in my area.
Thanks Again
Jerry
I see you have picked up a common misconception about synthetic motor oils. Synthetics are no "thinner" than any other equally rated motor oil. The rating system uses viscosity readings at specified temperatures to come up with the 30, 40, 50, etc. weight ratings. That 50 weight syn is basically the same "thickness" as that 50 weight dino oil. As for the first number in the multigrade rating, that is no longer a measure of viscosity at a lower temperature but is in fact a cold cranking measurement only.
The reason manufacturer's in the auto industry have gone to lower viscosities has to do with fuel economy ratings; a less viscous fluid requires less power to pump, therefore reducing parasitic power loss. They have been able to do this without sacrificing durability due to the many advances in materials, lubricants, and manufacturing tolerances over the past 30+ years. Modern engines running 5w20 will easily outlast the old iron running "heavier" oils. Think about it; we changed oil in our cars every 2000 miles in the old days, and 100,000 miles was pretty much the top end of the useful life scale (many engines needed major work long before that). Current automotive engines blow right past that 100,000 mile mark with 5,000 to 7,500 mile oil changes and very little else in terms of maintenance (change spark plugs one time, air filters every 20,000 or so).
Jerry