I don't know if this applies to the small diesels (non turbo/super charged), but the diesel generator
that I have a lot of experience running had 36 cylinders displacing 645 cubic inches each, and it had an interesting gear
driven (at low load) turbo (at full load) charger/compressor.
This diesel had very specific directions against running at low load (less than 30%).
The reason given for the load restriction was lower cylinder pressure at low load. The piston rings are designed to operate at rated load combustion pressures, this ensures normal lube oil consumption
rates. Light and no load operation promotes “souping”, which is excessive oil
escaping past piston rings into combustion chamber. Souping causes smoking exhaust
and potential exhaust
The recovery direction, if the engine was run at low load, was to follow that with at least a half hour at greater than 50% load.
Based on what I have seen running this engine, I would suggest that it is not a good idea to do extended runs at low load.