FYI on modern multigrade oils. The modern 15w40 oil actually has a thinner viscosity when cold than the factory recommended straight 20w! This ensures much better oil flow when the engine is cold hense better startup protection over the old factory recommendation.
Since the bottom end of my 216 has atleast 99k miles on it, probably more since the speedo is inop, those new machined tolerances have ben well worn down by now especially once the engine warms up & expands to it's normal operating temp. And as evidensed by several factors i.e. little loss of oil pressure, lower internal engine noise, no noticable increase of engine temps, the thicker oil is filling those increased tolerances with a slightly thicker film of protecting lubrication when warm.
I will agree that a brand new or freshly rebuilt 216 w/factory new tolerances should run a straight 20w or even better a 5w20 multigrade but in my case I ain't dealing w/brand new factory tolerances
re. 15w40 oil. this multigrade oil has quite an impressive track record of providing both new and old industrial engines proper long term lubrication. It's the standard oil for OTR diesels, heavy eqt machinery & agricultural engines and has been for decades. All ICE's require the cylinder walls to be coated w/a thin film of oil during operation and if this grade of oil didn't provide this it definitely wouldn't be the standard.
Oil can be an interesting subject. Theres too many variables so one size doesn't fit all.
Good luck
Dave
