Are lower OCI's better for timing chain wear even if analysis is good?

the winter rating decides how thin the base oil is. VII adds viscosity on both ends (cold and hot), only relatively more at the top end.

so, the 5w40 has thinner base oil and more VII
My understanding is that they would have the same(ish) base oil but the 5W30 would be the one with less VII, especially if we're looking at oils from the same category, eg a euro 5W30 A3/B4 MB 229.5 compared to a typical 5W40 of the same category.
No, the VII also raises the viscosity at the low temps, just not as much as on the high end.

For example, the same base oil that can make a 0W20 with added VII can produce a 5W-40. The same base oil that produces a 5W-20 can also produce a 5W-30. That's an analogy, there will be differences in base oil for a real life oil (why use the expensive PAO to make a 5W-40?)
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Not to discourage UOA testing but consider this;

Suppose the next series of UOA's shows a slight uptick in wear metals.

Is the increased wear metal content coming from cylinder/ring/piston-pin wear, crankshaft journal/bearing wear, cam wear, or from the timing chain?
If a person is willing to pay for a more extensive analysis through Polaris labs, they can tell you exactly what part the metal is coming from. It’ll cost a couple hundred bucks. I know several people that have done this on class 8 trucks. Money well spent considering engines can be upwards of $40,000 on class 8 trucks.
If a person is willing to pay for a more extensive analysis through Polaris labs, they can tell you exactly what part the metal is coming from. It’ll cost a couple hundred bucks. I know several people that have done this on class 8 trucks. Money well spent considering engines can be upwards of $40,000 on class 8 trucks.
Just curious but if there are several components in the engine with the same metal being used, then how could they ascertain the source of the wear?
Small, dense particles of soot are the general issue.

The timing chain wear test was the final test to be passed for the advent of SP/GF-6, and it took a while to crack that nut.

It is the dispersants, and as long as the dispersants are not depleated, then the oil should, in theory, hold up.

After all, SP/GF-6 also calls for capability of extending OCIs.

I say "probably not" to OPs query re shortening OCIs.
*How significant is soot content in a GDI engine with respect to engine wear (i.e. timing chain) ? My '17 Sonata GDI engine's oil is pretty dark by 2K ~ 3K miles .
I have wondered the same thing. As I've stated in other threads, I have 2 (Ford) Duratech's (which are based on the Mazda MZR engine). The 2.0 in my 14' Focus is GDI and the oil is beginning to darken about 2K into the OCI while the 2.5 in my 16' Escape is still clear looking when I change it (usually about 6K OCI). It help's that the 2.5 has a 5.7 qt. sump vs. 4.5 for the 2.0.
Because of the darkening (GDI soot I assume) and the smaller sump I'm hesitant to extend OCI's on the Focus where as I would have no concern doing so on the Escape using full synthetic.

PS: I haven't heard of any timing chain issues on MZR (or Duratech 4 cylinder) engines.
I believe what you are doing is ok. But if it’s me, I’d change out at 5km and never do another oil sample with the confidence I have done the best I can for my engine.
even looking at Redlines real synthetics you see better noacks with their heavier oils that start with heavier base oils BUT being a real synthetic i have seen that a PAO + or Ester 30w meets the 10W spec WITHOUT viscosity improvers!!! group III synthetics are good for the $$$$ but IMO + that of others they still fall short of the costlier PAO + Ester base oils.
Timing chains wear out over time, with all the early OCI's (like 1 to 4 thousand miles) , with these modern oils even synthetic blend is alot better than conventional from years past, you would be using more money on oil and still wear out the timing chain. Replacing it whenever it is worn enough is cheaper, if it is chain circuit is designed properly and a high quality chain is used, then it would take a VERY long time for the chain to die out.

My friend had a 1980s manual chevorlet truck with a timing chain and had to replace the chain at half a million miles, running 10w40 all the time and 15w40 sometimes.

If you live in an area where temperatures dont reach under 70 degrees Fahrenheit, 10w30 or 15w40 should do you well at 10k oci's.
There was a good study published on this exact topic sometime last year. Moly was found to have a fairly significant (positive) impact. High amounts of ZDDP appeared to make things worse. Found it:
The above linked study was rather interesting. However, I suspect the test was run using rather low viscosity oil. My speculation is that additives become the lubricant when oil viscosity is too low to prevent rapid wear. For over 100 years, industry has been using chains for power transmission, often in seriously heavy duty applications. So chain life was a major factor in operational costs, machine accuracy, down time and so on. Industry studied the problem and found the longest possible chain life required just two things. 1) 30 viscosity oil. 2) extremely clean oil. Despite what many here say, oil changes are the way to remove micro particulates from your engine oil. Unless one is performing particulate counts and knows the percentage of soot in the oil, extending OCI's beyond the severe service interval is risky. We've known about chain wear forever. This is nothing new and surprising. Timing chains have been failing for as long as they've been used. With wildly differing results on the very same engine models. The reason for early failures remains the same as it's ever been. My suggestion: Choose a quality synthetic oil of sufficient viscosity, change it frequently. The Ford Ecoboost chains that are failing take 25 man hours to change and the parts cost is near a $1000. That's nearly $4000 to replace chains, often before 100,000 miles. The oil change is cheap insurance.
I use M1 oils exclusively for 10K OCI (miles not KMs) and have put some 1,000,000 miles total on the last 5 Ford OHC engines, and have not had any chain or guide issues.
Some interesting information that looks quite technical showing improvements (measured, not subjective) in timing chain issues from using flush products (post #11) as well as shortened oil intervals in Europe on some lower TBN/longlife oils in some older VAG engines. Anyway, found it farting around over on vwvortex and thought it was interesting and relevant.

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