Hi fdcg27!, what I did was something that sounded reasonable at the time but probably incorrect, I took the FSM and look for the lowest "W" viscosity recommended for all situations and the highest hot vis. recommended for all situations too and looked for the best oil and compatible filter I knew back then that covered the "range" above, all ended being M1 oil and filter, mind you this was by the end of 1995, and knowing that synthetics can last up to twice the recommended OCI of a conventional oil I took the conservative approach of changing it every 5K miles since the manual recommended 3K miles for severe service. Now, although M1 5W50 says 50 it is actually around 40 in an engine asking for 30 and used in a hot climate. I do attribute the longevity of the engine to several factors, engine design, regular oil change with the best I knew, never mistreated or over stressed the engine while we had it and probably the most important factor, "luck". I'm in BITOG and asking questions because I want to know what I did right, what I did wrong and most important if I can do better. I never intended this to be another thick vs. thin debate, each I suspect have it's rightful use, If I were living in AZ and loading the van to it's limit plus pulling a heavy trailer I'll be using RL 20W50, but if I were in Alaska with a 5 miles commuting drive for the classic 9 to 5 job I'll probably be using a light 5W30 or even lighter with this wear and all. Maybe you don't remember but in one of my post I wrote that this engine is constantly turned off and on and many times the oil cools down a bit, so my special needs for this particular engine is a fast flowing oil at start up since as far as I know starting an engine constitute 90% of the overall wear with enough protection to keep it alive as long as I can, looking it from another angle I would like to know How much of the "over the top" metal to metal protection can I trade in favor of getting the oil faster to the parts in need of it and the reduction of work at the oil pump and related components.
George.