so i have a 20' forester with the 2.5 and have been using Mobil ep 0w20 w/out any issue of course except upon a cold start-up (overnight) i get a slight timing chain noise no biggie as the 2.5 in my 16' outback did it as well only worse/ they are known somewhat for this...anyway i changed to Quaker State Ultimate Durability 5w30 and it was whisper quiet upon start-up. question is why and how are the additives in Quaker State Ultimate Durability really making that much of a difference?? i would also think 0w20 would be flowing to the T.C faster than 5w30...just my unbiased experience with Quaker State Ultimate Durability in which finally made at least an audible difference in one of my vehicles..
1st time actually noticing a viscosity difference..
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My Accord always had vtc noise on startup with 0W20. Absolutely zero startup noise with 10W30.
Flow is irrelevant. The thicker oil quiets your chain noise due to a thicker film. It is good.
I can sure tell you in my tiburon the difference between a 30 and a 40 grade oil is huge. However most of this difference is noticeable power loss from the thicker oil and not the sound of the engine 
This is what I'm thinking. There's always some residual oil left on the chain components even after the engine is shut down for awhile. I think the thicker viscosity is helping quiet the noise.
The real question is whether that noise is problematic or indicative of increased wear (in the case of xw-20), versus no noise but thicker, more resistant to flow 30 weight oil at cold start.
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The 5W30 will be pumped at the exact same speed as the 0W20.
Whaaat? ... You'd think that positive displacement oil pumps are the most mysterious machines on Earth by so many thinking the forced pump flow changes with viscosity.
Is this due to the 5W vs 0W or 30 vs 20? If one were to extrapolate, would a 0w40 be noisier or quieter than the 5w30 (in theory, anyway).
Assuming "cold start up" is above 0F (for sake of conversation) couldn't there be a lot of similarity of the residual films in the bearings/chain components? Quaker State Ultimate Durability 5w30 and EP 0w20 have similar moly, boron, so I am assuming the answer lies in base oil or viscosity properties rather than additives. Thanks!
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Quaker State Ultimate Durability has 200+ ppm of molybdenum ( according to Shell) vs maybe 60+ ppm in M1.
But the thicker oil will leave a thicker film to be present at startup before that exact same flow speed reaches the tensioners, or whatever. Right?
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I’m guessing QS relies on mostly moly while M1 uses a bit of moly and other aw? Most of this beyond the simplistic goes way over my head
A base oil blend then an additive package is added to achieve an oil that meets or exceeds the requirements of the specs needed to meet the rating.
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