finally found the 5w-20 TSB...

[TheSilkySmooth]

Originally Posted by SilverGlow

If you are going for longevity for your engine, if you want it to last an absolute long time, then use 0w-20. Using 0w-20 will allow the engine to last longer then if you ran heavier oil.

This is because the lighter oil protects better during the time the engine wears the most: First 5-10 minutes of running after the first start in the morning.

At operational temperatures, there is a teeny tiny insignificant difference in engine wear between 20 and 30 and 40.

What kills engines is NOT running them at 212F on the freeway...what kills them is running the engines cold because cold means 10w-30 runs thicker then 0w-20 which means it circulates to the top and around all the internal engine parts SLOWER then 0w-20, and means more wear during the time engines wear the fastest: first 5-10 minutes of running for the day.

If you really know oil, understand how it works, you will see this is true. If you don't understand, you will have this dillusion that thicker protects better.

The only time you want to run the really thick stuff (40 weight for example) is if you are running hard, fast (racing or uphill under termendous load), and for long periods of time, in very hot weather. But for most of us, this is the exception and not the rule.

If you want your engine to last it's absolute longest, go 20 weight over 30 or heavier.

Have any studies to back this up? Just read on BTIOG that Engine wear is 5-7X higher during acceleration, then levels off. 5w-20 IS more stable than 5w-30 - a terrible multigrade. If the engine can run 5w-20 - run it. Fords seem to work well on 20wt. I wouldnt run it if there is excessive noise present on a warm motor - my 1nzfe is very noisey on a thin 5w-30 like syntec - so I am afraid of the 5w-20. Plus my fill cap says 5w-30 SL. Per the TSB, 5w-30 is the weight you HAVE to use.
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Aside: You need lube to get up in the ring pack and stay on the wear areas. This is NOT PAO group iv synthetic, a terrible lubricant but with good cold flow properties. So oil base stock magic makes a diff too. Conventional is better and most 20wt-er's swear by Grp II+ motorcraft SS.