Rethinking 5w-40 vs 15w-40 for my low use diesels

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They say it does but what do they know....yes I've used it in several applications for many years. It's not adding THAT much viscosity to a large sump. And "dry" is relative to normal everyday use...

"To complement this highly specialized additive package two proven frictional modifiers, Micron Moly®, a liquid soluble type of Moly and Schaeffer Mfg’s own proprietary additive Penetro. These two proven frictional modifiers once plated form a long lasting slippery tenacious lubricant film, which prevents the metal surfaces from coming into contact with each other."
Written by engineers and surface scientists, or salespeople? When you figure how liquid soluble moly plates on surfaces let me know.

I’ve been using 132 in various applications for almost two decades now. Won’t hurt to dose some in these vehicles regardless.
if you are only trying to save money, run your oil twice as long as you normally would. Take oil samples at your regular interval, change when needed. Best for you and the environment.
I have been pondering this same question myself. I have been running a synthetic 15W40 in my 642 and 606 power MB diesels and have done UOA on both. The 642 had a 10k oil change interval and the 606 was at 15k. During the winter it may sometimes get into the single digits, on rare occasion down to 0 or below. Usually a winter cold start would be 12-20F at the lowest. Chrome on the 642 was 4, Aluminum 10, Iron was 80. On the 606 after 15k miles, chrome was 4, aluminum was 7, Iron was 58. In the report blackstone said try 17k next time (which I wont). I am wondering if I am overthinking it, or if 15W40 flows too slow (especially in the 642) and is causing more wear on cold startup. I am thinking about at least switching it back to 5W40 and retesting it.
I was running 5w40 Rotella (T6) for the first few years on my 2016 6.7cummins.. last spring /summer I switched to 15w40 and I felt it sounded better both when cold and when warm. I don't run the truck in the winter, and I couldn't care less about the cost of the oil itself. Im going to use the 15w40 from now on because despite them both being rated 40 weight at operating temperatures I sense that the T4 is higher viscosity at 200degrees.
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