Simi
Thanks for that SBar marine inclusion. I've followed Tony's writings for decades and feel his take on load and RPM pretty decent advice snd fitting with realities of marine diesels.
The quoted article from Zimmerman is not entirely accurate for my Cat/Perkins Sabre or several other engine brands that have coolant cooled oil coolers. Why not?
With engines that have 180 degree thermostats and suitably sized oil coolers it is nigh impossible to achieve oil temperatures much above the thermostat settings. In my case, full load yields an oil temperature of 190 when coolant is at 185 or so. If one's engine is suffering from cooling issues at high loads, yes the coolant and oil temperatures can get well above the say 180F thermostat settings - but with an engine overheat looming.
Also it is not true that water will not be removed from oil until the oil temperature is above 212F. At say 185F water removal is just slower (but still adequate) not nil. For me the Zimmerman article has enough questionable statements that I'll label it "interesting."
Maybe one of our expert posters with Zimmerman experience could chime in.
When loaded at or above about 75%, on sea trials I routinely measure oil temperatures above coolant temperature, often 200-220F, which is ideal. On lightly loaded diesels I often see oil temp as low as 150F, which is squarely in sludge generating territory. Oil analyses confirm this. However, you are correct, if the oil uses a jacket water cooler, it will be regulated to emulate that of the coolant, which isn't a bad thing, I lose no sleep over oil running at 190 or 195.
Few diesels have oil thermostats, or jacket water coolers, for those that don't "cold" oil can be an issue in that it is more likely to generate sludge, which over time becomes varnish, which can restrict oil passages.
The article does parrot the line I've been hearing from boat salesmen for years, "modern common rail diesels don't suffer from light-loading issues". I don't believe that's true, as oil temperature, again unless thermostatically controlled, or elevated by jacket water cooling, remains an issue, as does combustion chamber temperature, conventional injection, common rail, tier III, IV, it does not matter. IIs it less of an issue on CR engines, yes, but it is not eliminated. Periodically running up to higher loads, my own guideline is 75% for 15 mins out of every 4 hours, will offset some of these issues.
Quantifying just how much of an issue chronic underloading can cause is challenging. I find it to be far more common on gensets, which are frequently under loaded, especially if sized for HVAC loads, when HVAC is not being used, it's impossible to avoid gross underloading. In these cases I encounter cylinder wall glazing, coking, blow-by and ring clogging, all of which lead to premature death for gensets, which die at 5-8000 rather than the 15-20,000 hours they are capable of. For propulsion engines this happens, more often on sailing vessels as engines are used to charge batteries, a horrible but often unavoidable scenario, but not as often. Most recreational power vessel diesels never reach their full lifespan, they die of accessory failure long before that, while commercial engines actually do reach this stage, "wearing out" the internally lubricated parts, and are often rebuilt because they are still comparatively young, and the bolt on bits are still serviceable and available from the manufacturer.
Finally, I don't believe this line is accurate, "Many passagemakers are fitted with engines that have just enough extra horsepower to stem a tide or buck the wind, and that are never intended to go much faster than their displacement speed. They are fuel-efficient, and they allow for great range. Most of the time, these engines are operating at 70 percent to 80 percent load at cruising speed."
"Many", "Just enough extra...", "70-80%"? More like a very few. Most trawlers and long range cruisers I inspect carry far more HP than they can effectively use.
My take on chronic under-loading
https://stevedmarineconsulting.com/the-perils-of-chronic-under-loading/
And related to this, the importance of proper break in
https://stevedmarineconsulting.com/properly-breaking-in-your-generator-and-why-this-is-important-2/
Why you were hardly past the break-in period. 
